Acta Geochimica最新文献

The Chayong Cu-polymetallic deposit is a recently discovered Cu-polymetallic deposit hosted in the Sanjiang Metallogenic Belt within the Tibetan Plateau of China to the northeast of the North Qiangtang terrane. The ore body occurs in siltstone and is controlled by a northwest-trending fault structure. According to the associations, assemblages, and cutting relationships between ore veins, the hydrothermal mineralization period can be divided into three mineralization stages: (1) a molybdenite mineralization stage, (2) a Cu-polymetallic sulfide stage, and (3) a quartz-carbonate stage. Two types of fluid inclusions (FIs), namely, liquid and vapor-rich inclusions, are present in quartz associated with sulfide minerals. Early-stage FIs are both liquid and vapor-rich, homogenized at temperatures ranging from 364.1 to 384.2 °C, and have salinities ranging from 0.70% to 9.60% NaCl equivalent (eqv). The middle-stage FIs are also both liquid- and vapor-rich, homogenized at temperatures ranging from 272.4 to 355.6 °C, and have salinities ranging from 0.53%–17.10% NaCl eqv. The late-stage FIs are liquid, homogenized at temperatures ranging from 209.4 to 255.3 °C, and have salinities ranging from 0.35%–6.87% NaCl eqv. The samples from the deposit have δ³⁴S values of − 21.8‰ to − 19.2‰ and − 5.5‰ to − 6.0‰, suggesting that sulfur was derived from the host sediments and magmatic fluids, respectively. The metallic minerals within the deposit have ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb values of 18.439–18.458, 15.656–15.679, and 38.772–38.863, respectively, suggesting that the metals were derived from the upper crust and orogenic belts. The samples from the deposit have δ¹⁸O_W values of 2.99‰–7.99‰ and δD_W values ranging from − 84.4‰ to − 73.9‰, indicating that the ore-forming fluids were magmatic and mixed with minor amounts of meteoric water. The ore-forming fluid of the Chayong copper polymetallic deposit was a high-temperature, medium- to low-salinity H₂O–NaCl–CH₄–N₂ ± CO₂ fluid system. The early high-temperature magmatic fluid, due to boiling, decreased in temperature, and via the mixing of meteoric water, gradually evolved towards the later-stage medium- to low-temperature and low-salinity fluid, causing molybdenite mineralization and forming copper polymetallic sulfide veins and quartz carbonate veins.

The Dahongshan Group, situated at the southwestern margin of the Yangtze Block, represents a geological unit characterized by relatively high-grade metamorphism in the region. This paper investigates the garnet-biotite schist from the Laochanghe Formation of the Dahongshan Group, employing an integrated approach that includes petrological analysis, phase equilibrium modeling, and zircon U–Pb dating. The schist is mainly composed of garnet, biotite, plagioclase, quartz, rutile, and ilmenite. Phase equilibrium modeling revealed the peak metamorphic conditions of 8–9 kbar and 635–675 °C. By further integrating the prograde metamorphic profile of garnet and geothermobarometric results, a clockwise P–T metamorphic evolution path is constructed, which includes an increase in temperature and pressure during the prograde stage. LA–ICP–MS zircon U–Pb dating and zircon Ti thermometry constrains the post-peak metamorphic age of 831.2 ± 7.2 Ma. Integrated with previously reported results, it is revealed that the southwestern margin of the Yangtze Block experienced a large-scale regional metamorphism during the Neoproterozoic (890–750 Ma), which is related to the collisional orogenic process. This may be associated with the late-stage assembly of the Rodinia supercontinent or with local compression and subduction processes during the breakup of the Rodinia supercontinent.

Beryl is the commercial source of beryllium and several varieties of it are valued as a gemstone. To contribute to understanding the mechanism of beryl formation, we carried out detailed geological, petrographical, and geochemical investigations on beryl mineralization occurrences in the Zabara-Wadi El Gemal (Z-WG) region. This region is an NW–SE trending tract that includes six beryl-hosting areas. The green gem variety of beryl (emerald) is restricted to phlogopite schist, pegmatite, and quartz veins. Prismatic hexagonal emerald crystals are well-developed in phlogopite schist and pegmatite. The gem variety emerald examined is sodic and Cr-dominant. It contains high concentrations of chromophore transition elements ordering Cr (up to 1511 ppm) > V (up to 242 ppm) > Sc (up to 245 ppm), giving rise to its vivid green color, reflecting mafic–ultramafic source contribution. Among the investigated emeralds, the Sikait area contains the highest BeO (av. 10.76wt.%) concentration. The compositional variability of emeralds is most likely attributed to the contribution from the host rocks. This is revealed by the examined emerald mineralization, for instance; the Abu Rusheid area (one of the best areas exposing rare metal-bearing granitoids) possesses the highest average of trace and REEs concentrations. In contrast, Um Kabu emerald has the highest contents of Co (av. 20 ppm), Ni (av. 299 ppm), MgO (av. 8.2wt.%), Fe₂O₃ (av. 3.12wt.%), and CaO (avg. 3.4wt.%) relative to other areas, which may be linked to contribution of ultramafic rocks exposed there. The proposed mechanism we suggest for emerald genesis is metasomatic interaction between felsic (intrusions, that are enriched with K, Na, Be, Li, and B, with mafic–ultramafic rocks that are enriched in Cr, V, Mg, Fe, and Ca. This interaction is marked by the formation of phlogopite schist, the growth of emerald crystals, and desilicated pegmatite.

The availability of lithium resources is of great significance for the development of modern technologies, as well as for civil and military industries. The Qinghai-Tibet Plateau is a region known for its abundance of lithium-rich salt lakes. However, the specific origin of lithium in these lakes is still unknown, which hinders the advancement of the lithium resource business in this region. To research this issue, this study involved the collection of 20 samples from Lakkor Co Salt Lake on Qinghai-Tibet Plateau, encompassing samples of surface brine, cold springs, fresh lakes, and recharge rivers. The composition of anions and cations in these samples was determined. Furthermore, the analysis extensively utilized the Piper three-line diagram, Gibbs model, and ion proportion coefficient. The findings of this study indicate that as the moves from the recharge water system to salt lake, there is a transition in water type from strong carbonate to moderate carbonate and weak carbonate, as well as Na sulfate. This research based on a similar source of both lithium and boron, utilized ion correlation analysis and boron isotope study in the Lakkor Co area, and analyzed the source and transporting process of lithium. The main origin of lithium in Lakkor Co is the dissolution of lithium-rich rocks, recharge water systems, and deep hydrothermal fluids. These findings are highly significant in enhancing the foundational data of lithium-rich brine resources in the Qinghai-Tibet Plateau and are beneficial for assessing the future development of such deposits.

An integrated method that implements multivariate statistical analysis and ML methods to evaluate groundwater quality of the shallow aquifers of the Djerid and Kebili district, Southern Tunisia, was adopted. An evaluation of their suitability for irrigation and/or drinking purposes is necessary. A comprehensive hydrochemical assessment of 52 samples with entropy weighted water quality index (EWQI) was also proposed. Eleven water parameters were calculated to ascertain the potential use of those resources in irrigation and drinking. Multivariate analysis showed two main components with Dim1 (variance = 62.3%) and Dim.2 (variance = 22%), due to the bicarbonate, dissolution, and evaporation and the intrusion of drainage water. The evaluation of water quality has been carried out using EWQI model. The calculated EWQI for the Djerid and Kebili waters (i.e., 52 samples) varied between 7.5 and 152.62, indicating a range of 145.12. A mean of 79.12 was lower than the median (88.47). From the calculation of EWQI, only 14 samples are not suitable for irrigation because of their poor to extremely poor quality (26.92%). The bivariate plot showed high correlation for EWQI ~ TH (r = 0.93), EWQI ~ SAR(r = 0.87), indicating that water quality depended on those parameters. Different ML algorithms were successfully applied for the water quality classification. Our results indicated high prediction accuracy (SVM > LDA > ANN > kNN) and perfect classification for kNN, LDA and Naive Bayes. For the purposes of developing the prediction models, the dataset was divided into two groups: training (80%) and testing (20%). To evaluate the models’ performance, RMSE, MSE, MAE and R² metrics were used. kNN (R² = 0.9359, MAE = 6.49, MSE = 79.00) and LDA (accuracy = 97.56%; kappa = 96.21%) achieved high accuracy. Moreover, linear regression indicated high correlation for both training (R² = 0.9727) and testing data (0.9890). This well confirmed the validity of LDA algorithm in predicting water quality. Cross validation showed a high accuracy (92.31%), high sensitivity (89.47%) and high specificity (95%). These findings are fundamentally important for an integrated water resource management in a larger context of sustainable development of the Kebili district.

Ozone (O₃) pollution has a profound impact on human health, vegetation development, and the ecological environment, making it a critical focus of global academic research. In recent years, O₃ pollution in China has been on a steady rise, with ozone emerging as the sole conventional pollutant to consistently increase in concentration without any decline. This study conducted a quantitative analysis of O₃ concentrations across 367 Chinese cities in 2019, examining spatial autocorrelation and local clustering of O₃ levels, and investigated the diverse relationships between human activity factors and O₃ concentration. The seasonal fluctuation of O₃ exhibited the “M-type” pattern, with peak concentrations in winter and the lowest levels in summer. The center of O₃ pollution migrated southeastward, with the area of highest concentration progressively shifting south along the eastern coast. Moreover, O₃ concentration showed a strong positive correlation with population density, road freight volume, and industrial emissions, suggesting that human activities, vehicle emissions, and industrial operations are significant contributors to O₃ production. The results provide comprehensive information on the characteristics, causes, and occurrence mechanism of O₃ in Chinese cities that can be utilized by global government departments to formulate strategies to prevent and control O₃ pollution.

The Early Cambrian represents a critical time period characterized by extraordinary biological innovations and dynamic redox conditions in seawaters. Nitrogen isotopic signatures of ancient sediments have the potential to elucidate the evolutionary path of marine redox states and the biogeochemical nitrogen cycle within the water column of the Early Cambrian ocean. While existing research on this topic has predominantly focused on South China, the exploration of other continental margins has been limited, leaving contradictory hypotheses untested. In this study, paired δ¹⁵N and δ¹³C_org analyses were performed on the Lower Cambrian successions from the Shiairike section (inner ramp) and Well Tadong 2 (deep shelf/basin) in the northwestern and eastern Tarim Basin, respectively. Our data from the Shiairike section reveal a discernible shift in the operation of different nitrogen cycles for the black chert-shale unit, also referred to as the black rock series in Chinese literature, of the Yurtus Formation (Fortunian stage to lower Stage 3). Oscillating δ¹⁵N values for its lower part are suggestive of alternating anaerobic assimilation of NH₄⁺ and denitrification/anammox. This is likely attributed to a shallow, unstable chemocline consistent with the upwelling and incursion of deep, anoxic waters during a major transgression. In contrast, aerobic nitrogen cycling, indicated by positive δ¹⁵N values of  >2‰, dominated the upper part alongside a reduction in upwelling intensity. On the other hand, the δ¹⁵N signatures of Xishanbulake and Xidashan Formations of Well Tadong 2, which encompass a time interval from the Cambrian Fortunian Age to Age 4, are indicative of N₂ fixation by diazotrophs as the major nitrogen source. The two studied intervals, although not time-equivalent, exhibit separated states of nitrogen cycling at least during the deposition of the Yurtus black rock series. The spatially different nitrogen cycling of the studied sections is compatible with a redox-stratified ocean during the deposition of the Yurtus black rock series. The build-up of a NO₃⁻ reservoir and aerobic nitrogen cycling in seawater was largely restricted to near-shore settings whereas anaerobic nitrogen cycling dominated by N₂ fixation served as the main nitrogen uptake pathway in off-shore settings.

The Saltpond Basin, situated within the South Atlantic margin of Ghana, is a significant area for petroleum exploration but has received relatively limited research attention. Previous studies have examined source rock composition, but data on crude oil organic chemistry are lacking, hindering understanding of the basin’s petroleum system and evolution. To address this gap, we analyzed biomarkers and stable carbon-isotope ratios in Saltpond Basin crude oil using gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry to elucidate organic matter source, depositional environment, and thermal maturity. Findings were compared with oils from the West African segment of the South Atlantic margin, namely the Tano Basin and the Niger Delta Basin, to identify potential correlations and gain insights into regional variations. Molecular and isotopic results unveiled a significant prevalence of organic matter derived from lower marine organisms. Patterns of organic matter deposition and preservation in Saltpond oil samples suggested a suboxic marine transitional environment, contradicting conventional understanding of terrestrial dominance in such settings. Moreover, the potential for degradation processes to obscure differentiation between terrestrial and marine organic matter origins underscores the complex nature of organic matter dynamics in transitional marine environments. Analysis of molecular thermal maturity indices suggested Saltpond oils were expelled from source rocks exhibiting thermal maturity at the early maturity stage. Correlation analysis unveiled genetic disparities among crude oils sourced from the Saltpond Basin and those from the Tano and Niger Delta Basin, primarily due to variations in source input and depositional environment conditions. Saltpond oil exhibits lower terrestrial organic input than Tano Basin’s crude oils, which also have less terrestrial input than Niger Delta Basin crude oils. Additionally, its paleodepositional environment notably differs from oils in the Tano Basin (anoxic transitional marine-lacustrine settings) and the Niger Delta Basin (suboxic–oxic terrigenous deltaic or marine or lacustrine environments). Thermal maturity range of Saltpond oil is comparable to oils in the Tano Basin but lower than oils in the Niger Delta Basin. These findings provide valuable insights into petroleum generation history and unique organic geochemical characteristics within the Saltpond Basin, essential for exploration, production, and environmental management efforts in the region. Furthermore, correlation studies provide evidence that distinct biological, geological, and paleoenvironmental conditions shaped various oil types in the West African segment of the South Atlantic margin.

Fe(III) has been proved to be a more effective oxidant than dissolved oxygen at ambient temperature, however, the role of Fe(III) in pyrite acidic pressure oxidation was rarely discussed so far. In this paper, in-situ electrochemical investigation was performed using a flow-through autoclave system in acidic pressure oxidation environment. The results illustrated that increasing Fe(III) concentrations led to raising in redox potential of the solution, and decreased passivation of pyrite caused by deposition of elemental sulfur. Reduction of Fe(III) at pyrite surface was a fast reaction with low activation energy, it was only slightly promoted by rising temperatures. While, the oxidation rate of pyrite at all investigated Fe(III) concentrations increased obviously with rising temperatures, the anodic reaction was the rate-limiting step in the overall reaction. Activation energy of pyrite oxidation decreased from 47.74 to 28.79 kJ/mol when Fe(III) concentration was increased from 0.05 to 0.50 g/L, showing that the reaction kinetics were limited by the rate of electrochemical reaction at low Fe(III) concentrations, while, it gradually turned to be diffusion control with increasing Fe(III) concentrations.

The Xingluokeng deposit is the largest granite-related tungsten deposit within the Wuyi metallogenic belt in South China. The Xingluokeng intrusion primarily consists of porphyritic biotite granite, biotite granite, and fine-grained granite. The deposit is represented by veinlet-disseminated mineralization with K-feldspathization and biotitization, alongside quartz-vein mineralization with greisenization and sericitization. This study investigates in-situ analyses of quartz compositions from both the intrusion and hydrothermal veinlets and veins. Trace element correlations indicate that trivalent Al³⁺ and Fe³⁺ replace Si⁴⁺ within the quartz lattice, with monovalent cations (such as Li⁺, Na⁺, and K⁺) primarily serving as charge compensators. Low Ge/Al ratios (< 0.013) of quartz from granites suggest a magmatic origin. The low Al/Ti and Ge/Ti ratios, accompanied by high Ti contents in quartz, suggest that the porphyritic biotite granite and biotite granite are characterized by relatively low levels of differentiation and high crystallization temperatures. In contrast, the fine-grained granite exhibits a higher degree of fractionation, lower crystallization temperatures, and a closer association with tungsten mineralization. Ti contents in quartz from quartz veins indicate Qz-I formed at temperatures above 400 °C, while Qz-II to Qz-V formed at temperatures below 350 °C. Variations in different generations of quartz, as indicated by Al content and (Al + Fe)/(Li + Na + K) ratio, suggest that Qz-I precipitated from a less acidic fluid with a stable pH, whereas Qz-II to Qz-V originated from a more acidic fluid with notable pH variations. Consequently, alkaline alteration and acidic alteration supplied the essential Ca and Fe for the precipitation of scheelite and wolframite, respectively, highlighting a critical mechanism in tungsten mineralization at the Xingluokeng deposit.