Genesis of the Dawadi potassium nitrate deposit in Lop Nor, China

Nitrate deposits are rare worldwide, especially potassium nitrate deposits; furthermore, their genesis remains disputed. There is a rare salt-lake type potassium nitrate deposit in the Dawadi area of Lop Nor at the eastern margin of the Tarim Basin, and the ore bodies show coexisting solid and liquid phases. Additionally, there are large sulphate-type potash deposits in the adjoining Luobei Depression, south of the Dawadi area. To determine why there are two different types of potash deposits in adjacent depressions with similar climates, field geological surveys were conducted and samples collected. It was found that the Tertiary clastic layer at the periphery of the Dawadi deposit was rich in high-salinity brine, with nitrate contents of up to 495–16,719 mg/L, much higher than those in the Luobei Depression, 1–35 mg/L. Additionally, a type of deep hydrothermal (Ca–Cl) brine was found in the fault zones, with nitrate contents of up to 8044 mg/L, dozens of times greater than that of ordinary groundwater. Using comprehensive analysis and research, we concluded that the Dawadi and Luobei depressions belong to different hydrological systems with no connection between them; thus, the two deposits belong to different metallogenic systems. Furthermore, groundwater played an important role in the mineralization of the potassium nitrate deposit, and a deep source may have been an important source of the ore-forming materials. The fault system widely developed in Lop Nor provides favorable channels for deep hydrothermal recharge, and the groundwater and deep hydrothermal brine could provide the source for the nitrate mineralization in the Dawadi Depression through water–rock reactions.

Dynamic variations in salinity and potassium grade of a potassium-rich brine deposit in Lop Nor basin, China

The Quaternary Lop Nor playa is the largest production base of potassium sulfate in the world. It has a mining history of more than 10 years, and its share in the Chinese potassium sulfate market is about 50% to-date. In this basin, the high-salinity potassium-rich brines are mainly contained in Middle Pleistocene–Holocene glauberite strata. Based on the monitoring of the underground brine table and geochemical analysis, this study reveals variations in the underground brine table and potassium-bearing grade before and after large-scale mining in the Lop Nor potash deposit. The results showed that the underground brine table and potassium sulfate grade decreased by varying degrees over sub-mineral areas after large-scale mining. The underground brine table declined by 8.5 m, on average, in the Luobei depression, by 6.4 m in the Tenglong platform and by 1.9 m in the Xinqing platform. However, the potassium-bearing grade showed the different trend. The Tenglong platform had the largest decline with average decreases in layers W1, W2 and W3 of 18.2%, 13.0% and 24.8%, respectively. In the Xinqing platform, the average decrease in layersW2 and W3 were 17.4% and 16.0% respectively. The Luobei depression decreases were relatively small (W1, W2 and W3 decreased 4.3%, 4.2% and 3.1%, respectively). This research provides a theoretical basis for the rational development and sustainable use of the potassium-rich brines in the Lop Nor basin.

Materials from the Vicinity of Lake Lop Nor in the Funds of the Central National Museum of Korea and Their Understanding in the Context of Contemporary Archaeological Studies in Xinjiang

Purpose. The article introduces and analyzes in detail the materials of the Bronze Age from the vicinity of Lake Lop Nor (Xinjiang, China), which are stored in the funds of the National Museum of Korea. The artifacts were obtained by the expedition to Xinjiang under the general guidance of the Japanese explorer and religious public figure, count Otani Kodzui. They are part of a special section of the famous “Otani Collection”. The Korean segment of this collection was completely described in the Republic of Korea in 2016, and now its analysis is presented in Russian for the first time. The materials of the Bronze Age constitute the most archaic part of the Xinjiang collection. This group includes 12 items: 4 woven baskets, 3 wooden masks with carvings of human faces, 2 ritual staves, 2 felt hats and one boot from a pair of leather footwear. Results. Analysis of the artifacts demonstrates analogies with the eponymous and most famous site of Xiaohe culture on the territory of Xinjiang – the Xiaohe burial ground at Lake Lop Nor. However, there were other complexes like Xiaohe which existed in ancient Xinjiang (for example, Beifang burial ground on the Keriya River). The authors note that the ornamental composition on the surface of woven baskets demonstrates similarity to the decor of the Andronovo culture’s ceramic vessels, and the iconography of wooden carvings of human faces is close to the images on the steles and plates of the Okunevo culture of Southern Siberia. Separate objects similar to both Andronovo and Okunevo cultures are also known to have been found on other sites of Xinjiang. Conclusion. The closest analogy to the described items from the funds of the National Museum of Korea is the Xiaohe culture materials. The question about the exact location of the site where the items of Xinjiang collection in Korea come from is still open. It requires additional research.

Extraction of K2CO3 from Low Concentration [K+] Solutions with the Aid of CO2: A Study on the Metastable Phase Equilibrium of K2CO3-Na2CO3-H2O Ternary System

Food grade (K2CO3 wt.%>99.0%, GB/T 25588-2010) potassium carbonate (K2CO3) has been extracted from low concentration [K+] solutions of K2CO3-Na2CO3-H2O, which refers to a subsystem of brine water in the Lop Nor Lake in West China. Procedures of the isothermal evaporation, crystallization, CO2 acidification, filtration, and calcination were employed to prepare the K2CO3. This research focuses on the phase study of metastable equilibria between K2CO3-Na2CO3-H2O and KHCO3-NaHCO3-H2O. The solubility, density, conductivity, and pH values were determined. Phase diagrams were plotted at temperatures of 298.2 and 313.2 K. At 298.2 K the ternary system of K2CO3-Na2CO3-H2O was found to have double salts in form of solid solutions Na2CO3·K2CO3·(6–12)H2O, which would hinder the process of getting pure K2CO3 by the means of isothermal evaporation. In this protocol the high-pressure CO2 was charged to the ternary carbonate solution, and the K2CO3-Na2CO3-H2O was moved to bicarbonate system KHCO3-NaHCO3-H2O. This quaternary system is of a simple co-saturation type of diagram, in which a solid solution (KHCO3·NaHCO3) was found to be greatly affected by temperatures. This finding affords efficient separation of KHCO3 from the KHCO3-NaHCO3-H2O solutions.