Origin and Circulation of Springs in the Nangqen and Qamdo Basins, Southwestern China, Based on Hydrochemistry and Environmental Isotopes

The Nangqen and Qamdo (NQ-QD) basins in China have very rich geothermal and brine resources. The origin and spatiotemporal evolutionary processes of its hot and saline springs however remain unclear. Geochemical and isotopic (18O, 2H, 3H) studies have therefore been conducted on the water from the geothermal and saline springs in the NQ-QD Basin. All saline springs in the study area are of the Na-Cl geochemical type while geothermal waters show different geochemical types. The oxygen and hydrogen isotopic compositions of the springs in the NQ-QD Basin are primarily controlled by meteoric water or ice-snow melt water and are influenced by rock-water interactions. It is found that the saline springs in the study area are derived from the dissolution of halite and sulfate that occur in the tertiary Gongjue red bed, while the hot springs in the QD Basin are greatly influenced by the dissolution of carbonatites and sulfates from the Bolila (T3b) and Huakaizuo (J2h) formations. Results from silica geothermometry and a silicon-enthalpy hybrid model indicate that the apparent reservoir temperatures and reservoir temperatures for the hot springs in the QD Basin range from 57–130°C to75–214°C, respectively. Deuterium analysis indicates that most of the hot springs are recently recharged rain water. Furthermore, the saline springs have a weaker groundwater regeneration capacity than the hot springs. Tritium data shows that the ranges of calculated residence times for springs in this study are 25 to 55 years, and that there is a likelihood that hot springs in the QD Basin originated from two different hydrothermal systems. The geochemical characteristics of the NQ-QD springs are similar to those of the Lanping-Simao Basin, indicating similar solute sources. Thus, the use of water isotope analyses coupled with hydrogeochemistry proves to be an effective tool to determine the origin and spatiotemporal evolution of the NQ-QD spring waters.

Hydrochemical Characteristics of Earthquake-Related Thermal Springs along the Weixi–Qiaohou Fault, Southeast Tibet Plateau

The Weixi–Qiaohou Fault (WQF) is considered an important zone of the western boundary of the Sichuan–Yunnan block, and its seismicity has attracted much attention after a series of moderate–strong earthquakes, especially the Yangbi Ms6.4 earthquake that occurred on 21 May 2021. In the present research, we investigate major and trace elements, as well as hydrogen and oxygen isotopes, of 10 hot springs sites located along the WQF, which are recharged by infiltrated precipitation from 1.9 to 3.1 km. The hydrochemical types of most analyzed geothermal waters are HCO3SO4-Na, SO4Cl-NaCa, and SO4-Ca, proving that they are composed of immature water and thus are characterized by weak water–rock reactions. The heat storage temperature range was from 44.1 °C to 101.1 °C; the circulation depth was estimated to range between 1.4 and 4.3 km. The results of annual data analysis showed that Na+, Cl−, and SO42− in hot springs decreased by 11.20% to 23.80% north of the Yangbi Ms5.1 earthquake, which occurred on 27 March 2017, but increased by 5.0% to 28.45% to the south; this might be correlated with the difference in seismicity within the fault zone. The results of continuous measurements of NJ (H1) and EYXX (H2) showed irregular variation anomalies 20 days before the Yangbi Ms6.4 earthquake. In addition, Cl− concentration is more sensitive to near-field seismicity with respect to Na+ and SO42−. We finally obtained a conceptual model on the origin of groundwater and the hydrogeochemical cycling process in the WQF. The results suggest that anomalies in the water chemistry of hot spring water can be used as a valid indicator of earthquake precursors.

Prospects for the development of geothermal energy supply

The paper addresses methodological and technological issues of building environmentally friendly and efficient energy supply based on geothermal energy sources. Geothermal potential in the world, accentuating that in Russia (areas of the Baikal natural territory) and Mongolia, is analyzed considering the possibility of its implementation in the thermal power industry. Geothermal areas of Central Mongolia are characterized by increased heat flows and occurrences of thermal waters. The most promising thermal spring occurrences are the Shivert, Shargalzhuut, Tsenkher, Otgontenger, and Khuzhirt, to name some of them. Currently, the thermal energy potential of the Khangai arched uplift in Central Mongolia is employed to heat industrial, agricultural, and civil facilities. There are also plans to consider the possibility of large-scale employment of thermal waters of the region for electricity generation. An example of using geothermal waters for electricity generation is given, and the possibility of establishing a heating system in the city of Tsetserleg based on a geothermal heat pump unit with a wind power plant is assessed.

Tungsten Accumulation in Hot Spring Sediments Resulting from Preferred Sorption of Aqueous Polytungstates to Goethite

Geothermal waters usually have elevated tungsten concentrations, making geothermal systems important sources of tungsten in the environment. To study the transport of tungsten in hot springs to hot spring sediment, which is one of the key processes for the release of geothermally derived tungsten to the surface environment, geochemical investigations of the hot springs and their corresponding sediments in Rehai (a representative hydrothermal area in southwestern China) and systematic laboratory experiments of tungstate and polytungstate adsorption onto typical iron-bearing minerals in hot spring sediments (i.e., pyrite and goethite) were conducted. The results demonstrate that considerable tungsten concentrations (i.e., not much less than 10 µg/L), formation of polytungstates under acidic conditions, and enrichment of iron oxide minerals represented by goethite are the prerequisites for extreme enrichment of tungsten in hot spring sediments (e.g., 991 µg/g in the ZZQ spring outflow channel). The absence of any of these conditions would weaken the immobilization of aqueous tungsten and result in higher mobility of tungsten in the hot springs and its further transport downstream, possibly polluting the other natural waters in and around Rehai that serve as local drinking water sources. This study provides an insight for identifying the key geochemical processes controlling the transport and fate of undesirable elements (in this case, tungsten) in geothermal systems.

Volumetric Properties for the Aqueous Solution of Yttrium Trichloride at Temperatures from 283.15 to 363.15 K and Ambient Pressure

To effectively develop the rare earth elements resources from the geothermal waters, it is essential to understand the volumetric properties of the aqueous solution system to establish the relative thermodynamic model. In this study, densities of YCl3 (aq) at the molalities of 0.08837–1.60639 mol·kg−1 from 283.15 K to 363.15 K at 5 K intervals and ambient pressure were measured experimentally by an Anton Paar digital vibrating-tube densimeter. Based on experimental data, the volumetric properties including apparent molar volume (Vϕ) and the coefficient of thermal expansion of the solution (α) of the binary systems (YCl3 + H2O) were derived. The 3D diagram (mi, T, Vϕ) of apparent molar volumes against temperature and molality was plotted. On the basis of the Pitzer ion-interaction model of electrolyte, the Pitzer single-salt parameters ( β MX 0 v , β MX 1 v , and C MX v ) for YCl3 and temperature-dependence equation F(i, p, T) = a1 + a2ln(T/298.15) + a3(T-298.15) + a4/(620-T) + a5(T-227) as well as their coefficients ai (i = 1–5) in the binary system were obtained for the first time. The values of Pitzer single-salt parameters of YCl3 agree well with the calculated values corresponding to the temperature-dependence equations, indicating that single-salt parameters and temperature-dependent formula obtained in this work are reliable.

BIOFUELS: A RETURN TO THE PAST OR A MODERN RENEWABLE SOURCE OF BIOENERGY

The analysis of research on biofuels is presented. In connection with the forecast of the depletion of fossil sources for energy production and their adverse effects on the environment, research and practical work on the use of renewable resources for these purposes is being carried out in different countries. Plant biomass, wind, sun, hydro resources, geothermal waters, etc. are considered. According to some data, wood biomass in the European Union from all renewable sources in 2012 was 50%. Among the suppliers of wood biomass in the world, short- cropped plantations of fast-growing tree species (poplars, willows, etc.) are gaining popularity. The European Union has adopted a plan to create 70,000 hectares of such plantations. In the Central Chernozem region of Russia, research on the creation and evaluation of the effectiveness of short- rotation plantations began in the mid-90s of the twentieth century. Studies have shown that on a plantation of Robusta poplar at the age of 4 years, with a 2-year rotation and a planting density of 20 thousand plants per 1 ha, the annual increase in absolutely dry biomass can be 11.5 t/ ha/year. After a long break due to the difficulties of the 1990s, these works were resumed only in 2015-2016. In accordance with the developed program, work has begun on the creation and research of experimental facilities both on the territory of Research Institute of Forest Genetics, Breeding and Biotechnology and on the lands of industrial forest enterprises. The best results on the growth of poplars in the reproductive areas were obtained in the Kulikovsky forestry of the Lipetsk region, where the annual shoots of poplars ‘Voronezh Giant’ and P. trichocarpa at the root-cutting plantation reached an average height of 157-183 cm.