Applied Geochemistry最新文献

Coastal aquifers, as the interface zone between ocean and land, are highly sensitive and vulnerable to seawater intrusion. This study presents the behavior of radium isotopes and their application to estimate the rate of seawater intrusion in a typical coastal city (Qinhuangdao, China). The hydrochemical results indicated that the coastal aquifers have Na–Cl type water with the lower Na/Cl ratios. The analysis revealed that the formation process of the chemical composition of groundwater was mainly the mixing of seawater and groundwater, while that of inland groundwater was dominated by mineral dissolution and cation exchange and adsorption. Groundwater of intruded aquifers contain significantly higher activities of radium than those of nearshore seawater and inland groundwater. The rates of seawater intrusion were estimated by using equation of the fate and transport of radium in 1–D transient groundwater flow system. In the calculation process, we ignored dissolution and co-precipitation and mainly considered mixing, alpha recoil and decay contribution for radium activity as sources and sinks terms of radium in coastal groundwater based on the characteristics of radium activity and ²²⁴Ra/²²⁸Ra ratio in groundwater. The recoil (P) was determined by the activity ratio of ²²⁴Ra to Th (²³²Th/²³⁰Th), while the retardation (R_f) was calculated from the steady-state radium equilibrium equation. The seawater intrusion rates were obtained by integrating ²²⁴Ra and ²²⁸Ra activities under different thorium ratios (²³²Th/²³⁰Th). The results show that the rate of seawater intrusion varies in a wide range at different locations, which are 0.17–1.03 (²³²Th/²³⁰Th = 0.67) and 0.11–1.01 (²³²Th/²³⁰Th = 1.25) m/d. The method of calculating seawater intrusion rate with radium isotope can obtain the rate of different parts of heterogeneous anisotropic aquifer, which also extends the application of radium isotope in hydrogeology.

The North Tianshan orogen consists of a series of thrust faults and is the most seismic region in China. In this paper, the characteristics of hot springs in the North Tianshan orogen are analyzed. Hydrochemical analysis of 13 hot springs and four mud volcanoes reveals that the cations of most hot springs are mainly Na⁺, while the anions are mainly Cl⁻.Atmospheric precipitation is the main recharge source for the hot springs in the study area, with recharge heights ranging from −9 to 2344 m. Heat storage analysis and trace element results showed deep fluid characteristics, which is consistent with deep circulation processes and regional extrusion pressure background. In addition, continuous measurements of six hot springs were conducted once every three days. The results showed that Cl⁻ and SO₄²⁻ concentration anomalies occurred before several earthquakes of M_L4.0 in the North Tianshan orogen. The hot springs SWQ, HTB, and WS, which have deeper circulation depths, show better responsiveness than X10, which has a shallow circulation depth. The deep circulation of hot springs increases fault sliding friction, which contributes to energy accumulation and strong seismogenesis, and participates in the seismogenesis process. Therefore, continuous monitoring of ion concentrations of deep-circulation hot springs can help identify effective precursor anomalies in the North Tianshan orogen.

The CO₂ preparatory methods implemented during carbonate-clumped isotope analysis for the acid digestion of carbonate with the goal of high sample throughput yielded multiple empirical relationships for the thermometry. These methods varied significantly from its original practice of carbonate reaction at 25 °C using sealed vessel method to automated quick performance acid drip or common acid bath method at 70 °C or 90 °C temperatures, respectively; these approaches differed noticeably. Technical development replacing primitive reaction protocols, introduced different reaction conditions, causing significant differences in the chemical reaction procedure and CO₂ trapping, which caused variation in the values of slope and intercept for the linear regression equations governing carbonate-clumped isotope(Δ₄₇) distribution with carbonate growth temperatures. These studies include the Δ₄₇ measurement and analysis of either laboratory-grown or natural carbonates with precise knowledge of their precipitation/depositional temperatures. However, the discrepancies in the existing universal calibration schemes remained poorly understood despite adopting an identical data correction protocol. This is explained here by the reaction kinetics and CO₂ collection methodologies adopted during experimentation. The present study investigated the slope and intercept values of the published carbonate clumped isotope thermometry equations expressed in the accepted Absolute Reference Frame (ARF in CDES) at 25 °C after accounting for the acid correction factor. We observe a systematic shift in the mean slope and intercept values of 0.0154(±0.007) and 0.153(±0.0686) ‰ for 70 °C reaction experiments and offset of 0.0181(±0.008) and 0.197(±0.079) ‰ for the experiments conducted at 90 °C by using the acid drip and/or Common Acid bath method, respectively from the slope and intercept values of the calibration equations proposed using sealed vessel method at 25 °C reaction temperature. The mean values for slope and intercept are compared using ANOVA and paired f-test. These correction factors for slopes and intercepts will allow the transformation of clumped isotope values at different temperatures into ARF scale at 25 °C and enable accurate deduction of temperature for carbonate samples. Correction factors proposed here account for variations in the sample preparation techniques arising due to different reaction temperatures, mechanisms and vapor pressure in the chamber for isotopic exchange reaction to happen for smaller or prolonged time intervals.

Radioactive nickels are significant environmental concerns because of their long half-lives (⁵⁹Ni = 76,000 years and ⁶³Ni = 100.1 years) and high proportions in nuclear wastes in the repositories. Therefore, the investigation of sorption and mobility of Ni at the disposal facility sites is important for the prediction and evaluation of radiological risks to the public. Herein, the batch sorption and column experiments were performed under various geochemical conditions using site-specific rock and groundwater samples collected at the Wolsong low and intermediate level waste (LILW) disposal facility site in South Korea. The batch sorption results revealed that the sorption of Ni was strongly affected by the pH. Approximately 20% Ni adsorbed at pH 5, which enhanced over 90% at pH > 8. The batch sorption results were used to develop the surface complexation model (SCM) to predict the Ni sorption and its mobility behavior. The non-electrostatic generalized composite (GC) SCM approach simulated the Ni sorption data well. We believe, our study can interpret and extrapolate the sorption and transport behavior of Ni in the underground repository conditions.

Identification of the conditions of circulation, mixing, origin and age of groundwater in the area of underground mining plants is necessary for the correct design of drainage systems, directions of mining exploitation and intensity of mining works. For this purpose, isotopic studies were carried out in the mines of the Legnica-Głogów Copper District (LGCD) in Poland, characterized by complex hydrogeological conditions. The observed values of δ²H, δ¹⁸O and concentrations of tritium, as well as chlorides, sulfates and main cations in 29 water samples taken from different lithostratigraphic levels (and a few historical results) were used to explain the spatial variability of the origin of groundwater flowing into the mines. A model of groundwater mixing in the mining area of the LGCD was developed. The results of the research indicate that, depending on the region, the LGCD mines contain Holocene and/or interglacial waters, pre-Quaternary waters as well as older waters, recharged in period of very warm climate - flowing into the mining workings from deeper geological strata. Isotopic studies together with the chloride content measurements confirmed the correctness of the conceptual model of groundwater circulation within the mines. Their results will be useful in further elaboration of the strategy related to dewatering and designing further mining activities.

In mineral potential mapping, supervised machine learning algorithms have shown great promise in delineating and prioritizing potential areas. However, since mineralization being a relatively rare geological event, most supervised machine learning-based models face substantial challenges in properly identifying prospective areas. Data sets with strongly imbalanced distributions of the target variable (deposits) and insufficient training data sets impose obstacles to these kinds of models which can significantly impact adversely on the performance of the models. Moreover, in some cases, negative training data sets as the non-deposit locations aren't really true negative data, which cause higher uncertainty in a mineral potential map. In this study, for handling these challenges the deep autoencoder neural network is adopted. The autoencoder can be trained to reconstruct geospatial data set in totally unsupervised manner and identify prospective areas based on the reconstruction error, where higher error corresponds with areas of higher mineral potential. In order to confirm the efficiency of the autoencoder algorithm in mineral potential modeling, the model was compared with a popular data-driven approach that assigned a weight to the evidence layer by using a concentration-area (C-A) fractal model and a prediction-area (P-A) plot, and combined them using a multi-class index overlay method. Receiver operating characteristic (ROC) curve, success-rate curve, and P-A plot were adopted to evaluate the predictive ability of Fe prospectivity models pertaining to the Esfordi district of Iran. Also, we use an area under the ROC curve (AUC) and partial AUC (pAUC) to quantitatively evaluate the overall and sensitivity performance of models, respectively.