Applied Geochemistry最新文献

Intersection-type uranium deposits refer to the uranium deposits that are located at the intersection of mafic dykes and silicified faults and are an important type of granite-related uranium deposits in South China. However, the genesis of these deposits still remain poorly understood. The Egongtang uranium deposit is a typical intersection-type uranium deposit in the Huangsha uranium ore district (southern Jiangxi) that bears a number of NWW-trending mafic dykes, thus providing an excellent opportunity to study the genesis of intersection-type uranium deposits. In this study, the mineralization age and genesis of this deposit were constrained using in situ zircon and pitchblende U-Pb geochronology, whole-rock geochemistry, and pyrite sulfur isotope data. The zircon U-Pb dating constrains the crystallization ages of 240.4 ± 1.3 Ma and 160.7 ± 1.6 Ma for granites in the Huangsha ore district. The samples (including altered and unaltered) of the granites are characterized by variable whole-rock U contents of 5.8–14.1 ppm and Th/U ratios of 2.4–7.7, which favor the crystallization of uraninite in the granites and suggest U leaching from the granites during alteration. In situ U-Pb dating on pitchblende from the Egongtang uranium deposit yielded a lower intercept age of 89.8 ± 1.1 Ma, indicating that the uranium mineralization took place at the Late Cretaceous. Pyrite associated with pitchblende has δ³⁴S values ranging from 1.6‰ to 3.8‰, suggesting a magmatic source. This study indicates that granites in this area might have represented the source of uranium for the Egongtang deposit, and that the uranium mineralization was probably related to the Late Cretaceous crustal extension in South China.

Selenate and selenite can sorb on AFm phases such as monosulfate, monocarbonate or hemicarbonate. Sorption and co-precipitation experiments were performed to determine their potential for the immobilization of two of the main aqueous species of selenium: Se^VIO₄²⁻ and Se^IVO₃²⁻. A preferential uptake by hemicarbonate over monosulfate, and a much weaker sorption on monocarbonate was observed for both Se(IV) and Se(VI). Increased sulfate and carbonate concentrations as present at higher pH lowered the uptake of Se(VI) and Se(IV).

Experimentally obtained sorption isotherms on hemicarbonate and monosulfate were reproduced with thermodynamic solid solution models, considering both surface sorption and interlayer bonding. For monocarbonate interlayer sorption was suppressed by the rigid structure and narrow interlayer distance. The observed limited uptake could be described by an anion exchange model on the outer surfaces only. This study shows that both anion exchange in the interlayer as well as sorption on outer surface sites can determine Se uptake by AFm phases.

Situated in the south edge of the Tibetan Plateau, the Himalayas is expected to receive direct anthropogenic Hg perturbations from South Asia, yet the measurements of atmospheric Hg deposition in the Himalayan region remain scarce. Here we report wet Hg deposition measured in the Yarlung Tsangpo Grand Canyon of the Eastern Himalayas, which is the deepest and longest canyon on earth. The precipitation Hg concentration (56.3 ng L⁻¹) and wet Hg deposition flux (84.7 μg m⁻² yr⁻¹) from the Motuo station were observed among the highest ever reported for the Tibetan Plateau. Together with analysis of principal component suggesting Hg was mainly clustered with anthropogenic ions and backward trajectories indicating 88.8% of air masses came from South Asia, our results show that transboudary pollution influences from South Asia could be largely responsible for the unexpectedly high levels of wet Hg deposition. Moreover, the wet Hg flux measurements (84.7 μg m⁻² yr⁻¹) are found an order of magnitude (∼13 times) higher than the GEOS-Chem estimates (6.8 μg m⁻² yr⁻¹), most likely due to the underestimation of transboundary Hg pollution influence by this model. Our study has important implications for better understanding Hg dynamics and verifying atmospheric Hg models in the Tibetan Plateau and Himalayas region.

Polymetallic Nodules from the deep sea are currently being targeted for mineral exploration as they are a significant resource for various critical metals. In addition to accumulating such metals, nodules are also known to adsorb naturally occurring radioactive nuclides. With the possibility of exploitation of nodules becoming more likely within the next years, it is important to assess the potential radiation exposures resulting from the handling of polymetallic nodules. In this study we present, for the first time, specific activities of all long-lived alpha, beta and gamma emitters from the natural decay chains of Uranium-238, Uranium-235 and Thorium-232, in bulk and surface material of the same nodules obtained from 10 locations within the Clarion-Clipperton Zone. The results show elevated specific activities for the nuclides Th-230, Ra-226, Pb-210, Po-210, as well as Pa-231 and Ac-227 in accordance with prior reported activities. However, in contrast to assumptions made in previous studies, our analyses show that Pa-231 is not in equilibrium with its daughter nuclide Ac-227. The emanation factor of Rn-222 for dry and water-saturated nodules has also been determined and is higher than previously reported. The results presented here are a key ingredient to assess human radiation exposure during the processes of polymetallic nodule mining, storage and beneficiation.

Basalt weathering can cause heavy metal enrichment in soils, and lithium isotopes serve as an effective tracer for this weathering process. However, the relations among weathering intensity, heavy metal migration, and Li isotope fractionation remain unclear. We conducted systematic examinations of a basalt weathering profile on tropical Hainan Island in China. The characteristics of mineralogy, elemental and Li isotopic geochemistry indicate that the profile has undergone changes from initial to advanced and ultimately extreme weathering stages. The corresponding dominant minerals are primary minerals, clay minerals such as kaolin-group, and the Al–Fe–Ti (hydro)oxides. The variations of Fe-group heavy metals within the profile are very similarly to that of Fe, exhibiting a pattern of loss-gain-loss. Newly formed secondary minerals preferentially incorporate lighter ⁶Li, leading to a gradual increase in Li content and a decrease in δ⁷Li. Due to the high δ⁷Li value of rainwater input, the ongoing impact of secondary mineral adsorption is partially counteracted. This results in the δ⁷Li of laterite and topsoil being maintained within a narrow range (−3.2‰ ∼ −1.9‰), despite the broader variation observed across the entire profile (−3.2‰ ∼ +2.8‰). Comparing basalt weathering profiles in different climatic zones reveals a very complex Li isotope behavior and its controlling factors. Therefore, it is essential to carefully evaluate the influence of atmospheric input, secondary mineral adsorption, dissolution, and redeposition processes on Li isotopes. Throughout the entire profile, Cr, Ni, and Cu exhibit enrichment relative to soil background values, indicating that the weathering of tropical basalt may pose potential environmental risks for these elements.

In the 1960s, ca. 3000–5000 tons of HCH residue were disposed of in an overburden dump at the Hájek kaolin/uranium mine site (Czech Republic). The dump leachate, which has a 136 μg/l average total content of hexachlorocyclohexane (HCH) isomers, discharges into a local creek and contaminates the ecosystem. A full-scale prototype for the treatment of dump leachate comprised three sequential stages: 1) permeable reactive modules filled with macro-zerovalent iron (mZVI), 2) a biosorption module and 3) an aerobic wetland module. After commissioning, HCH removal efficiency reached 95%, but decreased to 70% over the following 230 days, primarily due to the efficiency of the mZVI modules dropping from 76% to 39%. Hydrogeochemical analysis and geochemical modelling revealed that the reduction in efficiency was mainly caused by passivation of mZVI surfaces and clogging of mZVI pore spaces through precipitation of goethite, calcite and rhodochrosite, or siderite and magnetite instead of goethite where boundary conditions for O₂ differed. XRD analysis of the solid phase from the mZVI modules confirmed the geochemical modelling results. The major part of the precipitated products (46–66 wt%) comprised a ferric hydroxide amorphous phase, especially in the initial mZVI module inlet, with goethite the second most abundant precipitate (10–40 wt%). Siderite and calcite also mainly precipitated in the initial module inlet. In conclusion, mZVI appears to be a suitable reductant for HCH; however, the longevity of the ZVI-based treatment system was negatively affected by precipitates in the presence of high concentrations of iron, manganese and carbonate species.

The association of dissolved organic matter (DOM) with natural watershed backgrounds and anthropogenic activities is crucial for environmental assessment and sustainable development of basins. This study investigated the catchment-driven trend of DOM characteristics in the Hailar River basin, China. The results identified three fluorescent components through EEM-PARAFAC models: a terrestrial humic-like component (C1), a humic-like component related to microbial activity (C2), and a UVA humic-like component (C3), which were influenced by Cl⁻ and HCO₃⁻ derived from rock weathering. The contents of water-extractable organic carbon (WEOC) extracted from soils surrounding the watershed significantly correlated with the concentrations of DOC and COD_Cr. Furthermore, COD_Cr exhibits heightened sensitivity to precipitation and temperature fluctuations, revealing the synergistic effects of environmental factors and natural background. The hydrochemical composition and DOM characteristics are predominantly influenced by their origins from the Greater Khingan forests, indicating a catchment-driven trend of DOM in the studied river. What's more, COD in Hailar river basin was mainly controlled by refractory dissolved organic matter (RDOM). This research underscores the need for context-specific environmental standards rather than a “one-size-fits-all” approach and offers scientific insights and methodologies for the rational assessment of water quality and aquatic ecosystem health in similar riverine systems.

This study aims to comprehensively characterize the hydro-geochemical and isotopic features of the complex groundwater system in the Pordenone Plain (northeastern Italy). The area is an important industrial and agricultural area exposed to severe anthropogenic pressure and climate change, which put its water resources at risk in terms of quantity and quality, making it of high scientific and social interest. The hydrogeological setting of the Pordenone Plain has been previously simplified as a phreatic continuous aquifer in the High Plain that changes into a multilayered aquifer system towards the Low Plain. However, this study reveals significant lithological and structural heterogeneities in the High Plain that exert a strong influence on its subsurface hydrodynamics. All waters exhibit a Ca(Mg)–HCO₃ composition with relatively high Na–K values in the aquifers of the Low Plain likely related to cation exchange processes. Water stable isotopes (δ²H–H₂O and δ¹⁸O–H₂O) indicate that the deep aquifers in the Low Plain are confined by impermeable geological formations, such as clays and siltstones, which entirely restrict water mixing with shallower aquifers. Concurrently, tritium analysis provides evidence of slow recharge and flow rate. Three primary groundwater flows have been identified within the plain, as follows: 1) a surface flow that affects the unconfined or semi-confined aquifers of the High Plain hosted in gravelly sediments; 2) an intermediate flow fed by the pedemontane zone, which includes unconfined deep aquifers of the High Plain, semi-confined/shallow aquifers (at a depth of 40–50 m) located near the resurgence belt area and karst springs located in eastern pedemontane of the Cansiglio Plateau; 3) a deep flow fed by the mountainous zone that affects the deep confined aquifers of the Low Plain. A reliable hydrogeochemical conceptual model has been developed to explain the compositional variability of the studied waters, providing valuable insights for the sustainable management of groundwater resources in the Pordenone Plain.

Deposits enriched in rare earth elements (REEs) are abundant and diverse in mineralogy, but those of current economic value have extremely limited geographic distribution. Due to rapidly increasing demand and concerns about supply chain security, new and improved methods of prospecting, beneficiation, separation, purification, and recycling are needed. By overviewing the types and geographic distribution of REE deposits globally, their petrogenesis and major mineralogic assemblages, this review aims to deepen understanding of different types of REE deposits and distribution characteristics at the global level. Our review also seeks to provide a concise summary of important background information that is accessible to researchers from a variety of disciplines who are seeking to engage this rapidly expanding field.