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Rare-earth elements are widely used in the study of source tracing and geochemical characteristics, which can reflect the degree of influence of human activities on water environment. In order to reveal the additive effects of various human activities on the geochemical characteristics of rare-earth elements in the surface water environment, the content of rare-earth elements in the river in the coal grain composite area of eastern China was determined by inductively coupled plasma mass spectrometry (ICP-MS). The results showed that all water samples were alkaline, ΣREE content ranged 0.18–0.88 μg·L−1, with an average value of 0.28 μg·L−1. All the water samples showed significant enrichment of light rare-earth elements due to a combination of natural processes and external inputs. The spatial distribution and fractionation characteristics of rare-earth elements show that rare-earth elements (especially Ce) are prone to adsorption/complexation reactions with colloidal particles, resulting in their removal from rivers, Eu anomaly is related to plagioclase crystallization and human activities (coal development, agricultural production, urbanization process), and Gd anomaly is only related to human activities. The research results can provide scientific reference for revealing the distribution of rare-earth elements and geochemical environmental behavior in rivers environment under the superimposed influence of various human activities. [ABSTRACT FROM AUTHOR]

Travertines formed of crystalline crust have been widely reported, but there has not been focus on their geochemical characteristics. We therefore carefully conducted a series of geochemical investigations and U-Th dating on a travertine mound mainly composed of crystalline crust from Sobcha (southwest China) to determine their geochemical features and geological implications. The Sobcha travertines dominantly consist of granular crystals and fan crystals and show δ13C from 3.4‰ to 4.9‰ V-PDB, δ18O from −26.7‰ to −23.7‰ V-PDB, and 87Sr/86Sr from 0.712458 to 0.712951. When normalized to PASS, the Sobcha travertines exhibit MREE enrichment relative to HREE and LREE, HREE enrichment relative to LREE, and positive Eu anomalies. The δ13C signatures and mother CO2 evaluation of the Sobcha travertines show that the Sobcha travertines were thermogene travertines largely receiving mother CO2 from (upper) mantle (i.e., magmatic CO2) or a mixture of soil-derived CO2 and CO2 related to carbonate decarbonation. The 87Sr/86Sr of the Sobcha travertines is out of the 87Sr/86Sr ranges of local deposits exposed at Sobcha and surrounding areas but is well matched with the mean 87Sr/86Sr of Nadi Kangri volcanic rocks which cropped out to the northeast of the studied travertines (over 20 km away). This might indicate the important role of the Nadi Kangri volcanic rocks in suppling Sr to the studied travertines, but more studies are required. The LREE depletion compared to MREE and HREE in the Sobcha travertines was interpreted to be caused by the difference in geochemical mobility between LREEs and HREEs during water–rock interaction at depth, while the MREE enrichment compared to HREE was considered to be most likely inherited from reservoir/aquifer rocks. The positive Eu anomalies of the Sobcha travertines may result from very high reservoir temperatures and/or preferential dissolution of Eu-rich minerals/rocks (especially plagioclase). The Sobcha travertine mounds displays no or very slight vertical variations in δ13C, 87Sr/86Sr, and REE patterns, indicating the compositional stability of mother CO2 and paleo-fluids. However, a significant vertical increase in δ18O was observed and was explained as the result of gradual water temperature decrease related to climate cooling, self-closure of the vents, or mound vertical growth. The findings in this study might help us better understand the deposition of crystalline crust in Ca2+-deficient hot spring systems. [ABSTRACT FROM AUTHOR]

This article delivers a novel economic analysis of US dependence on China for rare-earth elements and sheds lights on how Western nations may exploit "limit pricing" to break China's global monopoly in rare-earth element production and refinement. This analytical framework, supported by a comprehensive literature review, the application of microeconomic and industrial organization concepts, and two case-study scenarios, provides several policy recommendations to address an important foreign policy challenge for the United States. [ABSTRACT FROM AUTHOR]

Phanerozoic sinter deposits have been reported globally, with their identification mainly based on sedimentological, petrological, and mineralogical studies. In this study, a detailed geochemical investigation, combined with sedimentological characterization, was conducted on the Wugonglilu siliceous deposit, a Cretaceous (106 Ma) sinter in NE China, to examine its genesis. The deposit is inferred as a siliceous hot spring deposit (sinter) owing to its geological setting in an epithermal gold-mining district, its morphologically variable microbial textures typical of subaerial sinters, and nearly pure silica composition. Three lithofacies were recognized in this study, including laminated to thinly bedded sinter, silica-cemented breccia, and epithermal vein, which represent deposits from three contrasting hydrothermal environments. The 87Sr/86Sr ratios of the sinter are similar to the bedrock through which the geothermal fluids passed, namely the Upper Triassic Dajiahe Formation (T 3 dj), a marine siliceous rock unit, and the Lower Cretaceous Datashanlinchang Formation (K 1 d), a rhyolite unit. Results indicate that both underlying units are possible Sr sources of the silica in the Wugonglilu sinter. The REE + Y (rare-earth elements and yttrium) patterns of the sinter exhibit significant variability, primarily due to terrestrial detrital contamination. Differential REE + Y contamination by terrestrial detritus was striking in the white and dark laminae/beds of the laminated to thinly bedded sinter. The white laminae/beds, generally less contaminated, were probably formed during the dry season, whereas the dark laminae/beds exhibiting greater detrital contamination were likely formed during the wet season. When excluding the samples strongly contaminated by detritus, the sinter exhibits Y anomalies comparable to Post-Archean Australian Shale (PAAS), and to the adjacent underlying K 1 d rhyolite and T 3 dj siliceous rock samples, indicating that these anomalies were not inherited from rocks dominating the reservoirs. Furthermore, the sinter shows a (Ce/Ce*) N range close to that of the underlying marine siliceous rock and rhyolite samples, reflecting that the (Ce/Ce*) N of the sinter is largely inherited from the reservoir rock(s). The overall REE + Y patterns of the sinter range from nearly flat to LREE-depleted, similar to some samples of the K 1 d rhyolite and T 3 dj siliceous rock units. However, most samples of the K 1 d rhyolite and T 3 dj siliceous rock display (Pr/Tb) N and (Pr/Yb) N higher than many studied sinter samples. This is likely because of the formation of strong HREE–carbonate complexes during groundwater migration. Based on these results, a generalized formation model of the studied sinter system was constructed. This study suggests that integrated sedimentological and geochemical investigations can aid in interpreting the genesis of sinter deposits, in particular the link between sinter deposits and corresponding reservoir rocks. [ABSTRACT FROM AUTHOR]

Ten representative limestone samples [six from Wangshan Formation (WL) and the other four from Gouhou Formation (GL)] were collected from outcrops of the northern Anhui Province, and REE concentrations in limestone were measured by ICP-MS. The depositional environment and source of the REE were analyzed, and the results implys that the total REE of samples are low compared with the recent marine sediments, which range from 9.61 to 54.18 mg/kg and an average of 22.93 mg/kg. The PAAS-normalized REE+Y patterns of limestone are characterized by (1) light REE depletion in WL and enrichment in GL with the values of (Nd/Yb) ranging form 0.65 to 0.91 and 1.12 to 1.46, respectively; (2) light negative Ce anomaly (0.85-1.02) and positive La anomaly (0.92-1.27); and (3) both Eu (0.91-1.23) and Y (1.42-2.38) expressing light positive anomaly. The character indicated that the depositional environment was oxygenated, with infection by the hydrothermal activity and contamination of detritus. [ABSTRACT FROM AUTHOR]

This study investigated the environmental geochemical characteristics of rare-earth elements (REEs) in surface waters in the Huainan mining area, Anhui Province, China. The REEs concentrations were determined by ICP-MS, and the inorganic species of dissolved REEs in the river and coal mining subsidence area water samples were calculated by using the Visual MINTEQ (version 3.1) code. On this basis, the distribution and geochemical characteristics of REEs in the surface waters were systematically analyzed, and the main inorganic species of REEs were investigated. The results showed the following: (1) The REEs concentrations in the surface waters were relatively low, ranging from 0.1361 to 0.3536 μg/L, and the average ∑REEs concentration was 0.2062 μg/L. Compared with light rare-earth elements (LREEs), heavy rare-earth elements (HREEs) were significantly enriched, with an average enrichment factor of 1.4642. Due to the interaction of high pH values and high cation concentrations, the ∑REEs content in the subsidence area water was significantly lower than that in the river water. (2) The distribution pattern of REEs in the surface waters normalized against the North American Shale Composite (NASC) showed that the REEs in the study area had different degrees of cerium (Ce) and europium (Eu) anomalies. The negative Ce anomalies were probably closely related to the pH conditions, whereas the positive Eu anomalies were mainly attributed to preferential chemical weathering and the dissolution of feldspar minerals. (3) The simulation results obtained by using Visual MINTEQ code showed that the dominant and typically inorganic complex form of REEs in the surface waters was carbonate complexes, and this form was one of the reasons for the enrichment of HREEs in the surface water., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

The chemical composition of the bottom sediments of the Amur River has been analyzed using modern analytical techniques. It was found that their composition and distribution patterns are controlled by several sources. The most probable sources for the bottom sediments of the studied area are siliceous magmatic or metasedimentary rocks. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.

REE and other trace elements in ores, wall rocks, alkaline volcanic rocks and diabase dikes have been determined in the Yinachang Fe-Cu-REE deposit. Comparative studies of REE and trace element geochemical characteristics of these geological bodies indicate that the ores and alkaline volcanic rocks contain abundant REE and Y (65.9 - 4633) x 10-6, with higher abundances of As, Mo, Nb, Co and U than those of the crust. Their chondrite-normalized patterns show a strong enrichment of LREE and a positive Eu anomaly, in contrast to those of the dolomites which are characterized by slight LREE enrichment and moderate negative Eu anomaly. The REE patterns of ores are similar to those of hydrothermal sediment cores in the East Pacific Rise, whereas the REE patterns of dolomites are similar to those of PAAS (Post-Archean Average Shale). In combination with the geological setting of the deposit, the primary ore-forming fluids might have higher REE and volatile elements, and might have been derived from mantle degassing, or the alkaline volcanic magmas. The Yinachang Fe-Cu-REE ore deposit is considered to be of volcanic exhalation-hydrothermal sedimentary origin. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Doushantuo Formation, South China, preserves a unique assemblage of what are probably the earliest metazoan fossils (sponges, cnidarians, and bilaterians) in the world that could contribute to a better understanding of early faunal evolution on Earth. The formation spans an interval of dramatic biological, chemical, and climatic change. In Weng''an mine in southwest China, extensive paleontological investigations show embryonic, larval, and adult animal fossils occur in the upper ore bed of the Doushantuo phosphorite, but no animal forms have been found in the lower ore bed. Taphonomy and experiments on fossilization suggest that no fauna lived on or in the lower ore bed as it was deposited. Rare-earth element (REE) data for the Doushantuo phosphorites in Weng''an document the paleoenvironmental condition under which the phosphorites were deposited. The shale-normalized REE patterns of the upper phosphorite bed (UPB) are characterized by “old” (Vendian–Early Cambrian) phosphorite patterns. The REE patterns of the lower phosphorite bed (LPB) are significantly different with less negative Ce anomalies and less LREE and HREE depletion. The REE characteristics suggest that the Doushantuo phosphorites record seawater condition at the time of sediment deposition and are not affected by subsequent diagenesis. The REE compositions of the Doushantuo phosphorites show that the marine depositional environment changed from anoxic in the lower ore bed to oxic in the upper ore bed. The uniquely diverse and abundant Doushantuo eukaryote fossil accumulations at Weng''an thus may be related to a change from anoxic to oxic bottom-water conditions. [Copyright &y& Elsevier]