Over the past century, electromagnetic exploration technology has evolved from direct current resistivity and induced polarization methods to a comprehensive geophysical system. Yet, in China's new mineral exploration phase, challenges like deep-mining needs, cultural noise, and weak 3D interpretation limit traditional methods. High-power-ultrahigh-power electromagnetic technology, by boosting transmission current, combats these issues. It enhances detection depth, enables 3D exploration, and drives technological and application innovation. This paper reviews the development of high-power-ultrahigh-power electromagnetic instruments and current research. It emphasizes that technologies like true 3D full-waveform IP collection and inversion, tensor CSAMT collection and inversion, and multi-parameter joint inversion of time-and frequency-domain EM methods can strengthen deep-target detection. Future research should tackle anisotropic 3D inversion, full-domain inversion with a field source, and extracting polarization and magnetization rates under complex constraints. These advances will propel electromagnetic methods toward greater depth, precision, and intelligence, supporting China's renewed mineral exploration efforts.

The deep mining of geological mineral information from geochemical exploration data has been a hot research topic in mathematical geology and geological big data. Despite China's abundant regional geochemical exploration data, the deep mining of geological mineral information from these data remains limited, necessitating a scientific, efficient, simple, and feasible data processing workflow and analytical methodology. This study investigated the Gaoqiao area in Huixian County, Gansu Province, China. According to the geological background and the theories of element properties and geochemical behavior, this study processed relevant element data to mine the geological mineral information in geochemical exploration data. It established preliminary mathematical models for the boundary delineation and lithofacies classification of intermediate-acid rock masses, and the boundary delineation of mafic volcanic rocks in the Gaoqiao area to scientifically guide geological mapping. It preliminarily established the target delineation model for tectonic altered rock-hosted gold deposits. The model's effectiveness was substantiated by seven newly delineated target areas with promising prospecting potential. The mineral inspection identified five ore occurrences, including four reported for anomalies related to mineralization, with two currently under provincial geological exploration. The results of this study show that by calculating and processing data based on the geochemical properties of elements, the hidden information in regional geochemical exploration data can be further mined to effectively guide and modify geological mapping, thereby enhancing mapping efficiency and quality. High-quality anomaly information can be further extracted from geochemical exploration data to effectively guide mineral prospecting in new areas.

To determine the optimal prospecting target in the Bishan area, Xianghuang Banner, Inner Mongolia, this study conducted a geochemical survey at 1∶10,000 scale. Using multivariable statistical analysis, this study analyzed 14 elements (i.e., Au, Ag, Cu, Pb, Zn, Mn, Mo, Li, W, Sb, Bi, B, Hg, and As) in soil samples from the study area. The results indicate that six elements, including Au, Ag, Pb, Zn, Li, and As, exhibited high enrichment degrees, suggesting their significant metallogenic potential. The anomalies of high-content elements are principally dictated by the outer contact zone between tuffs/tuffaceous volcanic breccias and granites in the Lower Permian Sanmianjing Formation. The ore-forming elements are primarily controlled by the NW-trending fault zone. Alterations like silicification, binarite, pyrite, galena, and sphalerite alterations serve as principal prospecting markers. Based on the geological conditions for mineralization in the Bishan area, this study delineated three composite anomalies and two prospecting targets, with Ag ore bodies discovered through engineering validation. Soil geochemistry proves crucial for the successful identification of polymetallic ore bodies, thereby providing a significant foundation for subsequent mineral exploration efforts.

A suite of dolomite-dominated carbonate reservoirs is developed in the Sinian Dengying Formation in the Huangling anticline in the eastern part of the intracratonic rift, western Hubei Province. Investigating the formation environment and genetic mechanism of dolomites is crucial for determining the developmental mechanism of carbonate reservoirs and facilitating conventional oil and gas exploration in the study area. This study employed various analytical techniques, including cast thin sections, cathodoluminescence thin sections, field emission scanning electron microscopy, carbon and oxygen isotope analyses of carbonate rocks, major and trace element analyses, whole-rock mineral analyses, and determination of the degree of order of dolomite. Using these techniques, this study analyzed the chemical composition and mineralogical characteristics of dolomites from the Dengying Formation on the periphery of the Huangling anticline. Furthermore, this study explored the formation environment, developmental mechanism, and modification process of dolomites. The results indicate that the dolomites from the Dengying Formation contained the same proportions of CaO and MgO molecules and low Sr content, aligning with the characteristics of penecontemporaneous dolomites. The analytical results of trace elements and carbon and oxygen isotopes confirm that the dolomites formed in a marine environment with low Fe and Mn contents. The average paleoseawater salinity (Z) of 128.41, average temperature of 21.32 ℃, and average diagenetic temperature of 49.36 ℃ created the favorable environmental conditions for forming penecontemporaneous dolomites. Additionally, the dolomite from the Dengying Formation exhibited significantly lower δ¹⁸O compared to the Dengyingian seawater, degrees of order ranging from 0.61 to 0.99, and a peak frequency distribution between 0.8 and 0.9, indicating that the dolomite experienced a progressively deepening burial modification process. The whole-rock mineral analyses reveal that the content of dolomite was positively correlated with its degree of order, suggesting that a high degree of dolomitization corresponded to a higher degree of order during burial modification. Therefore, this study holds that dolomites in the Dengying Formation were originally formed by penecontemporaneous dolomite. Through prolonged burial modification, micritic dolomite with a low degree of order experienced recrystallization, gradually transitioning into very finely crystalline/finely crystalline dolomite, accompanied by an elevated degree of order. Ultimately, dolomites of a penecontemporaneous-burial modification origin formed in the study area.

The Baiguo lithium-bearing porcelain stone deposit in Jiangxi Province, China is located in the southern Jiuling uplift within the Jiuling rare metal metallogenic belt. This large altered granite-hosted lithium-bearing porcelain stone deposit was discovered by the Geophysical and Geochemical Exploration Brigade of Jiangxi Bureau of Geology using geochemical exploration methods and assessed using geological methods. The prospecting process in this study involved the following aspects: identifying the potential prospecting area through regional geochemical exploration, pinpointing the prospecting target based on the 1∶50,000 stream sediment survey, delineating the lithium anomaly range and morphology based on the 1∶10,000 soil survey, determining the cause of anomalies through follow-up geochemical surveys, defining the spatial distributions of ore bodies through trenching exploration and drilling engineering, and ascertaining the occurrence state and selectivity of lithium based on experimental tests. This prospecting process demonstrates the fast, direct, cost-effective, and efficient characteristics of geochemical exploration methods and their superiority and significance in mineral exploration. Notably, to achieve satisfactory prospecting results, the geochemical exploration for lithium should attach great importance to the geochemical enrichment patterns of lithium, the scientific interpretation of anomalies, and the close association with geological work.

This study aims to further clarify the characteristics of uranium deposits and faults in a uranium mining area in Xingyi City, thereby laying a solid foundation for subsequent drilling operations. Soil radon measurements were conducted using the FD216 environmental radon meter. The data obtained were analyzed comprehensively to determine the content and distribution of radon in the soil, delineate the anomaly halos of soil radon, and refine the properties of concealed faults. Furthermore, the metallogenic characteristics of uranium deposits were examined, combined with geological and geochemical exploration data. This study revealed a strong correlation between soil radon content and fault strike. The most significant radon anomaly zones are located in the southwest and central-northeast sides. Uranium deposits in the study area occur in fault fracture zones and are associated with strata. The uranium exploration target might be located within the fault zone in the first member of the Middle-Lower Triassic Jialingjiang Formation.

The Shitai area in southern Anhui Province, China is located in the eastern part of the Xiushui-Ningguo carbonaceous-siliceous-argillaceous rock-hosted uranium metallogenic belt. The frequent activity of fault structures in this area contributes to great uranium mineralization potential. To explore the uranium resource potential in the Shitai area, this study conducted 1∶50 000 ground-based gamma-ray spectrometry. Accordingly, this study extracted metallogenic information using traditional statistical methods and difference analysis of uranium content, followed by the analysis of the distribution characteristics of radioactive elements. Then, this study analyzed the radioactive anomalies in the four members of the Hetang Formation based on the spectra and geological profiles. The analytical results revealed that the highest uranium content occurs in the first member of the Hetang Formation. By combining field geological surveys and microscopic petrographic analyses, this study further investigated the geological characteristics of the first member, as well as their potential relationships with uranium mineralization. The results indicate that the Hetang Formation serves as the primary uranium source in the Shitai area, with its first member identified as the main ore-bearing layer. This member is rich in ore-forming materials including organic matter, clay minerals, and pyrite, creating favorable conditions for uranium enrichment. The in-depth research on the target layer will provide technical guidance for exploring the same type of uranium deposits in this area.

The conventional inversion of anisotropic media is often constrained by assumptions of narrow-angle incidence and weak changes in stratigraphic properties.Moreover,the prediction of rock elastic parameters typically involves linear inversion and indirect fitting,leading to less accurate and reliable inversion results of petrophysical parameters for anisotropic formations.Hence,this study derived the petrophysical models of Young's modulus,Poisson's ratio,and fracture parameters for vertical transverse isotropy(VTI) media.Based on the precise VTI reflection coefficient equation,this study proposed a Bayesian anisotropic nonlinear direct inversion method,constrained by the L₁ norm,to predict the brittleness and fracture parameters of shale gas reservoirs through direct inversion.The proposed method yielded satisfactory application results in a study area of shale gas in Southwest China,offering a novel technique for characterizing shale gas reservoirs.

Log-seismic error correction serves as a primary method for determining Thomsen's compressional-wave anisotropic parameters of vertical transverse isotropy(VTI) media.This method is also an essential processing technique for obtaining accurate depth-migrated images.Conventional log-seismic error correction involves determining the log-seismic errors at well locations and then directly applying planar interpolation to correct the depths of seismic horizons.However,the conventional method can lead to structural distortions and anomalous values of anisotropic parameter δ in areas with significantly varying formation thicknesses.To address this issue,researchers typically manually edit and smooth the anisotropic parameter field and the anisotropic velocity field,consuming considerable manpower and time.Hence,this study proposed a structure-oriented log-seismic error correction method that incorporates the concept of log-seismic error coefficient.The proposed method utilizes formation thicknesses as constraints to perform planar interpolation for log-seismic errors.Moreover,it employs a strategy of sequential calculation and interpolation for log-seismic errors from shallow to deep formations.It yielded log-seismic error distribution values that better conform to formation thickness variations and more stable δ values,without anomalous values.Therefore,the proposed method effectively avoids structural distortions induced by log-seismic error correction while saving manpower and time in practical projects.

To address the challenges in predicting superimposed thin sandstones in lacustrine basins,this study proposed a technical workflow for their prediction using the seismic meme inversion(SMI) method.First,an initial inversion model was constructed using log curves from sample wells selected based on seismic waveform similarity.Second,the initial inversion model was iteratively optimized in a Bayesian framework to yield high-resolution SMI results.Third,the SMI results were integrated with low-frequency inversion results to yield high vertical resolution while effectively characterizing the lateral superimposed patterns and boundaries of sand bodies.Case studies demonstrate that the SMI method achieved a prediction accuracy of 2 m to 3 m for superimposed thin sandstones.The coincidence rates for calibration and validation wells reached 91.5 % and 85.2 %,respectively,confirming the effectiveness of the SMI method and the high precision of the inversion results.Overall,this study provides an effective technical approach to predicting superimposed thin sandstones in lacustrine basins.

High-velocity salt domes and steeply dipping structures in subsurface media pose challenges to conventional imaging methods.In conventional seismic exploration,multiples are usually treated as noise to be suppressed or eliminated.However,due to their long propagation paths and smaller reflection angles within subsurface media,multiples show a wider imaging range and richer information on subsurface structures.Since seismic interferometry enables accurate prediction of multiples,the reverse time migration(RTM) of multiples based on seismic interferometry is crucial for imaging complex subsurface structures.Based on the analysis of the fundamental principles of seismic interferometry,this study derived the corresponding equations and algorithms.Furthermore,this study proposed a multiple prediction technique based on seismic interferometry.By circumventing conventional multiple processing methods,this technique enhances imaging efficiency, providing a research basis for subsequent RTM of multiples.To address the significant crosstalk noise in conventional RTM,this study innovatively utilized seismic interferometry to explore the RTM of order-divided multiples.Finally,this study proposed a RTM method for order-divided multiples based on seismic interferometry,effectively mitigating the problem of crosstalk noise in multiple imaging.Numerical experiments show that compared to the RTM of primary waves,the RTM of multiples exhibited significant improvements in imaging pre-salt structures.The RTM of order-divided multiples based on seismic interferometry could further suppress the crosstalk noise in conventional RTM,enabling accurate imaging of complex pre-salt structures and improving imaging resolution.

With the continuous advancement of oil and gas exploration in China,the focus of seismic imaging has gradually shifted from large-scale overall imaging to small-scale complex structure imaging.Due to the inherent limitations of seismic wave propagation,small-scale and highly steep complex structures pose challenges such as difficulty in capturing interface reflection information and weak reflection energy.Consequently,conventional surface seismic imaging methods struggle to achieve accurate imaging of these targets.The seismic interferometry method can render the virtual observation system closer to the target area,improving the imaging resolution of complex interfaces, and achieving high-precision target-oriented imaging.This study conducted a theoretical derivation of the seismic interferometry mechanism and forward modeling of small-scale models.By comparing the generated interferometric gathers with actual reference gathers,this study verified the accuracy of the seismic interferometry method.Subsequently,this study applied the method to the backpropagation(BP) gas cloud model and a highly-steep structure- thin interbed model for numerical tests.The imaging results were finally compared with conventional reverse time migration(RTM) results,demonstrating that the seismic interferometry method enables high-precision imaging of deep complex structures.

Offset and source weight constitute critical factors influencing the data acquisition of transient Rayleigh surface waves. Hence, it is necessary to examine the characteristics of dispersion spectra derived from surface wave data acquired under different offsets and source weights. This study investigated the influence of the two critical factors on dispersion spectra through theoretical analysis and numerical simulation. Based on field experiments, this study delved into the characteristics of dispersion spectra from surface wave data collected at various excitation locations of seismic sources with different weights. To address the discrepancies in dispersion spectra caused by varying source locations during the data acquisition of transient surface waves, this study proposed a superposition and fusion method for multi-dispersion spectra, significantly enhancing the effectiveness of surface wave detection results.

Seismic waves, particularly their high-frequency components, will undergo energy attenuation during subsurface propagation. This results in a low signal-to-noise ratio (SNR) within the high-frequency band, significantly reducing the accuracy of seismic exploration for deep oil and gas. To enhance the SNR of deep seismic data, this study employed the time-frequency analysis technique to describe the time variations of signal frequency based on the non-stationary characteristics of seismic signals. Accordingly, this study proposed a method for suppressing deep high-frequency noise based on time-frequency analysis. Considering the stable and similar time-frequency characteristics of effective signals and the uncertain and random high-frequency interference, this study proposed an adaptive threshold selection strategy based on correlation analysis. This strategy involves extracting the time-frequency characteristics of effective signals from an advantageous frequency band and comparing them with the time-frequency characteristics within the high-frequency band. Subsequently, feature-constrained attenuation was applied to time-frequency spectra in the high-frequency band, thereby suppressing high-frequency noise. Theoretical models and actual data processing results demonstrate that the proposed method can effectively suppress high-frequency noise and significantly enhance the SNR of deep seismic data.

The electrical resistivity tomography (ERT) method has become the primary geophysical technique for landslide structure investigation. However, the complex terrain of landslides and the impacts of collapsed surface features render it challenging to arrange survey lines orderly along a straight line in practice. This leads to deviations in the calculations of apparent resistivity. To minimize the impacts of irregular survey lines on the final results, this study developed a scheme for the 3D inversion of measured data. Specifically, this scheme minimized 3D grid subdivision by identifying the rectangle enclosing the minimum area of complete survey lines. Meanwhile, this scheme suppressed the changes in model parameters in the vertical direction by increasing the regularization parameters along the vertical direction of the survey lines. Numerical simulation results indicate that, compared to the traditional 2D inversion scheme, the proposed 3D inversion scheme can significantly improve the identification accuracy of the sliding zone. The measured results of the Baishuihe landslide have verified the effectiveness of the proposed method.

This study conducted the forward modeling of a 3D good conductor model under a uniform half-space background to investigate its response characteristics in a plane electromagnetic wave survey. The electromagnetic anomalies of a three-dimensional good conductor are primarily caused by the secondary field generated by static charge accumulated at interfaces. Consequently, higher relative resistivity differences between the target conductor and the surrounding rock correspond to greater response anomalies. Additionally, a smaller distance between observation electrodes and the target conductor is associated with greater relative response anomalies. Changes in the horizontal and vertical dimensions of a conductor pose different impacts of anomalies. Specifically, variations in vertical thickness have minor impacts on the anomalies. When a conductor has similar dimensions in the horizontal direction, its apparent resistivity response curve resembles a two-layer D-type sounding curve, with the relative anomalies intensifying as the horizontal sizes increase. However, in the case of significant differences between the two dimensions in the horizontal direction (with the larger dimension being at least eight times the smaller), the response curves observed in the directions of the larger and smaller dimensions differ. Notably, the apparent resistivity response curve observed in the direction of the larger dimension resembles a three-layer H-shaped sounding pattern characterized by high, low, and high values sequentially. In addition, the relative anomalies of apparent resistivity are generally more than two times those of phase, with apparent resistivity anomalies following the static effect law in the vertical direction. Specifically, apparent resistivity anomalies in high frequencies tend to extend to low frequencies, creating favorable conditions for anomaly identification. Therefore, apparent resistivity anomalies are more conducive to anomaly identification for good conductors.

Large-depth induced polarization sounding requires power supply with long wires and high current. This results in the oscillation of the turn-off waveforms, which greatly affect the accuracy of induced polarization (IP) measurement. To address this issue, this study first constructed a simulation model for electromagnetic induction caused by the long wires for high-power IP transmitters and proposed a method to eliminate IP electromagnetic coupling using an RCD absorption circuit. Then, using the optimal absorption circuit algorithm, the parameters of the optimal absorption circuit were calculated. Afterward, the optimal absorption circuit of the high-power 30 kW IP transmitter was designed, and the simulation results indicate that the optimal absorption circuit effectively mitigated the oscillation of turn-off waveforms. Finally, based on the optimal absorption circuit, a high-power IP transmitter prototype was developed. An AB/2 configuration with a large electrode spacing of 1 500 m was deployed in an area of Shanxi Province. The full turn-off waveforms at four measurement points were repeatedly observed under an emission current of 10 A. With a maximum standard deviation of polarizability estimated at 0.02, the accuracy of the transmitter met the requirements of relevant specifications.

A typical channel turbidite system is developed in the deep-water area of the Lower Congo Basin,West Africa,establishing this area as a significant target for deep-water oil and gas exploration.Turbidite bodies in this area are characterized by strong heterogeneity and a complex reservoir distribution.Traditional methods show limited turbidite body identification accuracy and reservoir prediction ability,failing to support efficient exploration.This study investigated the channel turbidite system in this area based on the deep-water gravity flow theory.It established feature identification models for four kinds of channel turbidites at different scales.The models integrate the turbidite depositional site,accommodation space geometry,internal turbidite characteristics,and the rock,log,and seismic facies obtained through drilling.Furthermore,guided by the principle of facies-controlled reservoir distribution,new composite elastic parameters were constructed based on an improved ray-path elastic impedance inversion method.These parameters provided enhanced resolution for turbidite sandstone reservoirs,enabling a quantitative prediction of such reservoirs.Validation with post-test wells demonstrates high accuracy and favorable application outcomes.Overall,this study serves as a foundational guide for oil and gas resource assessments and well placement in similar deep-water areas.

Seismic velocity model accuracy significantly influences the quality of depth-migrated images.However,a quantitative analysis and clear understanding of this relationship remain lacking.Based on the seismic images of ultradeep fault-controlled fractured-vuggy reservoirs in the Tarim Basin,this study constructed a depth-domain numerical velocity model that approximates the conditions of subsurface media.The 3D seismic forward modeling was performed using a seismic acquisition and observation system for practical production.Different interval velocities within the numerical model were smoothed and used to quantitatively analyze their effects on reverse time migration(RTM) images based on identical parameters.Using seismic simulation data as input,the isotropic and anisotropic depth-domain velocity models were constructed following a standard industrial workflow.A quantitative analysis was subsequently conducted to analyze the differences of the constructed models and corresponding migration images from the numerical velocity model and its RTM image across different intervals and for various geological features.Overall,this study quantitatively analyzes the velocity accuracy of different velocity types in various intervals and its influence on migration imaging, obtaining several clear insights.

Based on the high-precision and high-quality data of eight heavy metals obtained from the 1∶250,000 multi-purpose regional geochemical survey in Fujian Province, this study investigated the topsoils (depths: 0~20 cm) throughout the province, with reference to the Environmental Quality Standard for Soils (GB 15618—2018). A geochemical assessment method for soil environmental quality based on individual/composite indices, matching the structural characteristics of the assessment standard, was developed to first assess the environmental quality of topsoils across Fujian Province. The results indicate that the topsoils in Fujian Province are dominated by strongly acidic and acidic soils, representing 36.5% and 57.89% of the total area in the province, respectively. The soils for prioritized conservation cover 91.06% of the total area, suggesting overall high soil environmental quality in the province. The over-limit ratio of 8.94% for soil heavy metals in the province is significantly below the total over-limit ratio of 16.1% in China. The element with the highest over-limit ratio is Pb, accounting for 4.95%, followed by Cd, accounting for 2.84%. In contrast, elements like Zn, Hg, Cu, As, Ni, and Cr show minimal over-limit ratios. Regarding the spatial distribution characteristics of topsoil elements, zones with over-limit Pb, Cd, Zn, Cu, As, and Cr are primarily distributed in the metal or non-metal sulfide deposits/ore occurrences/mineralized spots within the Wuyishan metallogenic belt and their surrounding areas. Zones with over-limit Hg are primarily distributed in the junction zone between Youxi and Dehua counties, as well as in cities along the coastal area of Fujian Province. The zone with over-limit Ni is predominantly located in the geological background area of the Fotan Formation basalts and olivine basalts in the northeast of Zhangpu County. Overall, the soil environmental quality is higher in the coastal area compared to the inland area. The assessment results of this study fill the gap in the geochemical assessment of soil environmental quality in Fujian Province, first providing the comprehensive geochemical assessment data of soil environmental quality for the province. These data, revealing the environmental quality of soil resources in Fujian Province, serve as fundamental geochemical data for scientific research in related fields and for constructing the geological information engineering big data platform for Fujian Province. Overall, this study provides a decision-making reference for soil environment management, territorial space planning, and the construction of the national ecological civilization pilot zone (Fujian) in Fujian Province, holding significant scientific value.

This study analyzed the distributions, enrichment characteristics, and health risks of heavy metals (Cd, Cr, Hg, As, and Pb) in soil-crop (maize, rice, and wheat) systems in the Shizuishan area, Ningxia Hui Autonomous Region. The results indicate that the contents of heavy metals in the soils were below national background values, with the geoaccumulation index indicating an overall clean soil environment. Different crops showed significant differences in their ability to enrich heavy metals, with Cd and Pb being more enriched in wheat, and As and Hg being more enriched in rice. Moreover, significant correlations were observed between soil pH and heavy metal enrichment coefficients. With an increase in pH value, maize exhibited markedly increased enrichment coefficients for Cr and As, whereas rice manifested a notably decreased enrichment coefficient for As. Soil organic matter inhibited the ability of crops to absorb and enrich heavy metals by reducing the bioavailability of heavy metals. The health risk assessment reveals a high non-carcinogenic risk index for children via the hand-to-mouth route. The As content in some samples exceeded the limit specified in food safety standards, requiring targeted monitoring. The results of this study provide a scientific basis for soil contamination control and safe crop production.

To investigate the contamination, source, and ecological risk of soil heavy metals in a typical industrial town in Shandong Province, China, this study collected 499 topsoil samples from the study area from August to October 2022. The contents and spatial distributions of heavy metals like Hg, Cd, As, Pb, Cu, Cr, Zn, and Ni in the samples were analyzed using classical statistics and spatial interpolation methods. The source apportionment of heavy metals in the study area was explored through the principal component analysis (PCA). The contamination levels of heavy metals in the study area were assessed using the contamination index method. The results indicate that the average contents of Hg, Cd, As, and Pb in soils all exceeded their background values in Yantai City, and high-value zones were observed for all eight elements, indicating various degrees of enrichment. The analysis of coefficients of variation reveals that except for Ni, other heavy metals were significantly influenced by human activities. The PCA suggests that Cd, Pb, Cu, Zn, and Cr originated primarily from industrial and traffic sources. As and Hg were predominantly derived from industrial, agricultural, and domestic sources, while Ni was primarily from natural soil parent materials. The analyses based on the single-factor contamination index, geoaccumulation index, and Nemerow contamination index show that apart from Hg and Cd, other soil heavy metals in the study area exhibited no or slight contamination overall, demonstrating that the study area was principally contaminated by Hg and Cd. The potential ecological risk assessment suggests that the overall heavy metal contamination posed a minor risk level. A few sites with relatively severe contamination were primarily located around the industrial area. The waste gas, wastewater, and industrial residue generated by industrial activities constituted the dominant factor influencing the enrichment of heavy metals in surrounding soils. Overall, soil heavy metal contamination in the study area was at a moderate to low level, with some metals, particularly Hg and Cd, severely exceeding standard levels, warranting attention. It is recommended to strengthen the monitoring of heavy metals in soils around the industrial area, and adopt scientific and reasonable measures to ensure sustainable soil utilization.

This study aims to determine the selenium (Se) background values of oils along the northern margin of the Qinghai-Tibet Plateau and serve the utilization of Se-rich resources, as well as the prevention and control of Se deficiency risks. To this end, this study systematically collected 8 273 surface soil samples and 2 190 deep soil samples, analyzed and tested the Se content and other relevant indicators, and examined the response relationships between soil Se and factors such as soil type and physicochemical properties. The results indicate that the surface and deep soils exhibit Se background values of 0.188×10^-6 and 0.153×10^-6, respectively. High Se background values are identified in the Menyuan Basin, the Xining Basin, the northern part of Qinghai Lake, and the Lagrange and Daban mountains. The highest Se background values occur in soils with the weathering materials of red and coal-bearing clastics of the Paleogene Xining Group as parent materials. The Se background values exhibit a negative correlation with pH and a positive correlation with the contents of organic matter and iron-aluminum oxides. Se in soils tends to accumulate in woodlands, grasslands, peat-rich marsh soils, and meadow soils. The study posits that the soil-forming parent materials with Se background values, including red and coal-bearing clastics of the Paleogene Xining Group, serve as the primary factor controlling the formation of Se-rich soils, and the secondary controlling factors include carbon-rich forests, grasslands, meadow soils, and marsh soils. The transportation by water streams and sedimentary transformation of these controlling factors contribute to the formation of the spatial distribution pattern of localized Se enrichment in the soils of the northern margin of the Qinghai-Tibet Plateau.

Based on the summary of the genetic types and elemental characteristics of national selenium (Se)-rich land, this study explored the arid saline lacustrine sedimentary type Se-rich land. According to the requirements for the delimitation and identification of natural Se-rich land, this study assessed and delimited the Se content, environmental quality, and fertility of soils in Hongshuiquan Township, Ping'an District, Haidong City, Qinghai Province. The results indicate that the soils in the Hongshuiquan area are alkaline, exhibiting a high background level of available Se. Specifically, the content of soil Se ranged from 0.037 mg/kg to 6.544 mg/kg, with an average of 0.352 mg/kg. The contents of Cd, Hg, Pb, and Cr in the soils did not exceed their contamination risk screening values for agricultural land. Additionally, soil As shows potential risk in local plots. In terms of fertility status, the soils exhibit abundant available phosphorus and potassium, and moderate nitrogen and organic matter. Based on the above results and the designated values for Se-rich land in the alkaline soil area, while excluding soil contamination risk zones and considering the continuity, scale, and development and utilization of plots, this study delimited 43 591 mu (1 mu=0.066 7 hectares) of natural green Se-rich land in the Hongshuiquan area, including 13 513 mu for direct agricultural use, and 30 078 mu for potentially utilizable forest land and grassland. Considering local conditions, this study suggests the development of the integrated agriculture and animal husbandry industry in the Hongshuiquan area, centering on the delimited zones and extending to the peripheries with moderate Se content. Planting grain crops and green forage grass in the delimited zones, surrounded by free-range grazing, forming an industrial layout of land with high Se content for grain crops and land with moderate Se content for grazing. Overall, this study holds critical reference significance for further exploring Se-rich land resources in Qinghai Province, scientifically planning the selenium industry, highlighting location advantages, and efficiently transforming resource value.

The contamination of soils and groundwater caused by landfill leachate is increasingly prominent. Given the distinctive electrical properties of leachate, such as low resistivity, high polarization, high time constant, and low-frequency correlation coefficient, this study performed three-dimensional finite element numerical simulations of landfills using the spectral induced polarization (SIP) method. The aim is to explore the theoretical effects of this method in detecting landfill leachate. First, this study conducted forward modeling for typical geoelectric models using the algorithm developed in this study. The result revealed a maximum relative error between the numerical and analytical solutions of less than 2.5%, demonstrating the algorithm's accuracy and effectiveness. Second, the parameters of the SIP model were set based on the actual electrical characteristics of landfills, ensuring that the numerical simulations closely reflected actual conditions. Finally, SIP anomaly responses were compared and analyzed for landfill leachate leakage under different scenarios. The results indicate that the leachate locations can be accurately delineated using the apparent complex resistivity's phase and apparent dispersion, regardless of whether landfills are equipped with high-resistivity impermeable walls. For leachate plumes of the same scale, shallower locations corresponded to more pronounced anomaly morphologies of apparent complex resistivity's phase and apparent dispersion. Compared to the direct current resistivity method, the SIP method can detect richer underground electrical parameters, achieving better application effects in detecting landfill leachate.