Crystallization path of salts from brine in Zabuye Salt Lake, Tibet, during isothermal evaporation

Zabuye Salt Lake in Tibet, China is a carbonate-type lake, rich in Li, B, K and other useful trace elements that are of great economic value. We studied the concentration behavior of these elements and the crystallization paths of salts in the brine at 25 C, based on an isothermal evaporation experiment. The crystallization sequence of the primary salts from the brine is halite - aphthitalite - zabuyelite - sylvite - trona and thermonatrite in accordance with the metastable phase diagram. In the experiment, zabuyelite was precipitated in the early stage in the brine at 25 degrees C. Potassium was precipitated as sphthitalite in the intermediate stage and as sylvite in the late stage, while boron was concentrated in the early and intermediate stages and precipitated as borax in the late stage

Characterization of a eukaryotic picoplankton alga, strain DGN-Z1, isolated from a soda lake in inner Mongolia, China

Dagenoer Soda Lake is located on the Xilinhaote plateau in Inner Mongolia at an elevation of 1289 m. Blooms of one predominant kind of picoplankton algae were found in the lake throughout the year. A strain of this picoplankton alga, designated DGN-Z1, was isolated in axenic culture. Its cells are spherical or oval, 2-3 in diameter; it grows optimally at 0.5-1 M NaCl, and tolerates pH values from 7 to 12. Phylogenetic analysis based on sequence similarity of the 18S rRNA gene suggested that it belongs to the green algal species Picocystis salinarum

Fluorine speciation and origin of Early-Middle Triassic bentonite deposits in Sichuan Basin, South China

Fluorine (F) is one of the most important environmentally harmful elements released by volcanic activity, and the bentonite deposits that formed from volcanic ashes are potentially harmful to the environment. However, the mechanisms governing F-rich bentonite formation and its F speciation composition remain enigmatic. The F-rich bentonite deposits are widely distributed in the Early-Middle Strata of the Sichuan Basin, South China. Detailed mineralogical and geochemical studies were conducted on the bentonite deposits from five sections of the Sichuan Basin. X-ray diffraction (XRD) analyses indicate that the F-rich bentonites mainly contain quartz, carbonates (calcite and dolomite) or gypsum, and clay minerals, while the clay minerals are dominated by illite and illite/smectite (I/S). Clay mineralogical studies suggest that bentonites were transformed from volcanic ashes during diagenesis by smectite illitization. The major and trace element distribution in F-rich bentonite deposits altered from volcanic ashes is most likely derived from felsic magmas, and alteration of the parent rocks (e.g., rhyolites) to bentonite is associated with leaching and subsequent removal of F. The total fluorine content (FTOT) of the bentonite samples ranged from 1,162 mg/kg to 2,604 mg/kg (average = 1773 mg/kg), well above the average FTOT contents of soils in the world. The results of the sequential extraction experiments show that the highest content is residual-fluorine (Fres), followed by carbonate-fluorine (Fcar) with a mean value of 1,556 mg/kg and 186 mg/kg, indicating carbonate is an important F sink in bentonite deposits. The average fluorine value of organic fluorine (For), Fe/Mn oxide-fluorine (Ffm) and exchangeable fluorine (Fex) are relatively low with an average value of 17.5 mg/kg, 6.8 mg/kg and 4.1 mg/kg, respectively. However, water-soluble fluorine (Fws) has a mean value of 4.0 mg/kg, which is higher than the corresponding average value in soils in an area susceptible to endemic fluorosis in China. Based on the characteristic of fluorine speciation, the fluorine in bentonite deposits may pose a risk to the environment. This study makes an important contribution to a better understanding of the characteristic of fluorine speciation in bentonites and the formation mechanism that governs fluorine enrichment in bentonites

Origin of Minerals and Elements in the Late Permian Coal Seams of the Shiping Mine, Sichuan, Southwestern China

Volcanic layers in coal seams in southwestern China coalfields have received much attention given their significance in coal geology studies and their potential economic value. In this study, the mineralogical and geochemical compositions of C19 and C25 coal seams were examined, and the following findings were obtained. (1) Clay minerals in sample C19-r are argillized, and sedimentary layering is not observed. The acicular idiomorphic crystals of apatite and the phenocrysts of Ti-augite coexisting with magnetite in roof sample C19-r are common minerals in basaltic rock. The rare earth elements (REE) distribution pattern of C19-r, which is characterized by positive Eu anomalies and M-REE enrichment, is the same as that of high-Ti basalt. The concentrations of Ti, V, Co, Cr, Ni, Cu, Zn, Nb, Ta, Zr, and Hf in C19-r are closer to those of high-Ti basalt. In conclusion, roof sample C19-r consists of tuffaceous clay, probably with a high-Ti mafic magma source. (2) The geochemical characteristics of the C25 coals are same as those reported for coal affected by alkali volcanic ash, enrichment in Nb, Ta, Zr, Hf, and REE, causing the C25 minable coal seams to have higher potential value. Such a vertical study of coals and host rocks could provide more information for coal-forming depositional environment analysis, for identification of volcanic eruption time and magma intrusion, and for facilitating stratigraphic subdivision and correlation

Dalangtan Saline Playa in a Hyperarid Region on Tibet Plateau: II. Preservation of Salts with High Hydration Degrees in Subsurface

Based on a field expedition to the Dalangtan (DLT) saline playa located in a hyperarid region (Qaidam Basin) on the Tibet Plateau and follow-up investigations, we report the mineralogy and geochemistry of the salt layers in two vertical stratigraphic cross sections in the DLT playa. Na-, Ca-, Mg-, KCaMg-sulfates; Na-, K-, KMg-chlorides; mixed (K, Mg)-chloride-sulfate; and chlorate and perchlorate were identified in the collected samples. This mineral assemblage represents the last-stage precipitation products from Na-K-Mg-Ca-Cl-SO4 brine and the oxychlorine formation from photochemistry reaction similar to other hyperarid regions on Earth. The spatial distributions of these salts in both stratigraphic cross sections suggest very limited brine volumes during the precipitation episodes in the Holocene era. More importantly, sulfates and chlorides with a high degree of hydrations were found preserved within the subsurface salt-rich layers of DLT saline playa, where the environmental conditions at the surface are controlled by the hyperaridity in the Qaidam Basin on the Tibet Plateau. Our findings suggest a very different temperature and relative humidity environment maintained by the hydrous salts in a subsurface salty layer, where the climatic conditions at surface have very little or no influence. This observation bears some similarities with four observations on Mars, which implies not only a large humidity reservoir in midlatitude and equatorial regions on Mars but also habitability potential that warrants further investigation

Dalangtan Saline Playa in a Hyperarid Region of Tibet Plateua-III: Correlated Multiscale Surface Mineralogy and Geochemistry Survey

We report the first multiscale, systematic field-based testing of correlations between orbital scale advanced spaceborne thermal emission and reflection radiometer visible near-infrared (VNIR)/shortwave infrared (SWIR) reflectance and thermal infrared relative emissivity and outcrop scale Raman spectroscopy, VNIR reflectance, X-ray diffraction (XRD), and laser-induced breakdown spectroscopy (LIBS) mineralogy and chemistry in a saline dry lakebed. This article is one of three reports describing the evolution of salt deposits, meteorological record, and surface and subsurface salt mineralogy in Dalangtan, Qaidam Basin, a hyperarid region of the Tibet Plateau, China, as potential environmental, mineralogical, and biogeochemical analogues to Mars. We have successfully bridged remote sensing data to fine scale mineralogy and chemistry data. We have defined spectral end-members in the northwestern Qaidam Basin and classified areas within the study area on the basis of their spectral similarity to the spectral end-members. Results of VNIR/SWIR classification reveal zonation of spectral units within three large anticlinal domes in the study area that can be correlated between the three structures. Laboratory Raman, VNIR reflectance, XRD, and LIBS data of surface mineral samples collected along a traverse over Xiaoliangshan (XLS) indicate that the surface is dominated by gypsum, Mg sulfates, Na sulfates, halite, and carbonates, with minor concentrations of illite present in most samples as well. Our results can be used as a first step toward better characterizing the potential of orbital reflectance spectroscopy as a method for mineral detection and quantification in salt-rich planetary environments, with the benefit that this technique can be validated on the ground using instruments onboard rovers

Modeling and Optimization of Wireless Signal Transmission Characteristics of Mine Roadway Based on 3D Ray-Tracing Method

The mine roadway is a special restricted space where wireless signals cannot freely propagate. The research on the transmission characteristics of wireless signals in mine roadways is of great significance for establishing a safe and reliable underground communication system. In this context, the transmission characteristics of wireless signals with a frequency of 700 MHz in the roadway are studied using the three-dimensional (3D) ray-tracing method. The calculation of the vertical dimension of the roadway is increased, and a roadway model is established to more comprehensively reflect the transmission characteristics of the signal in the roadway. The results show that the field strength in the near-source region is high, the attenuation is fast, and the fluctuation is strong, while the waveform in the far-source region gradually stabilizes and decays. The signal strength is related to the number of reflections; the more reflections, the weaker the signal strength. When the transmitting end is close to the edge of the roadway wall, the signal attenuation is faster and the fluctuation amplitude is stronger. The signal strength in the roadway is affected by the cross-sectional size of the rectangular roadway, and the larger the length and width dimensions, the better the waveguide can be formed in the roadway. The simulation results of wireless signal transmission in the roadway are compared with the measured results from a coal mine in Ganhe, Huozhou, and the results show that the model established by the 3D ray-tracing method can predict the field strength distribution of wireless signal. This study provides a theoretical foundation and practical guidance for improving the reliability and quality of wireless signal transmission in mine tunnels. Future research directions can further optimize algorithms, enhance transmission rates, and improve interference resistance to meet the needs of wireless communication in mine tunnels

Mineralogical and Geochemical Characteristics of Triassic Lithium-Rich K-Bentonite Deposits in Xiejiacao Section, South China

Widespread alteration in the Early–Middle Triassic volcanic ash of the Xiejiacao section, south China, has resulted in significant occurrences of lithium-rich K-bentonite deposits with economic potential. Detailed mineralogical and geochemical investigations of Li-rich K-bentonite deposits from the Xiejiacao section of Guangan city, South China, are presented here. The X-ray diffraction (XRD) data and major element chemistry indicates that the Li-rich K-bentonite deposits contain quartz, clay minerals, feldspar, calcite and dolomite, and the clay minerals are dominated by illite and ordered (R3) illite/smectite (I/S). The concentrations of major and trace elements in Li-rich K-bentonite deposits altered from volcanic ashes are most likely derived from felsic magmas, associated with intense volcanic arc activity. The composition of the clay components suggests that the Li-rich K-bentonite deposits are probably altered from the smectite during diagenesis, whereas smectite is mainly formed by submarine alterations of volcanic materials and subsequently the I/S derived from the volcanogenic smectite illitization. Moreover, accurate determination of the structure in I/S reveals that the temperatures reached by the sedimentary series are around 180 °C with a burial depth of ~6000 m. The widely distributed lithium-rich clay deposits strongly indicate widespread eruptions of volcanic ashes in the Early–Middle Triassic, which released huge amounts of volcanic ash. Lithium fixed in the illite and I/S is considered to have leached from the volcanogenic products by a mixed fluid source (i.e., meteoric, porewater and hydrothermal fluids). These Li-rich clay minerals in the marine basin contain economically extractable levels of metal and are a promising new target for lithium exploration