The northeastern margin of the Linyi uplift is located at the eastern end of the Luxi Block and immediately adjacent to the Yishu fault in the east. The main structural framework of the study area is controlled by the NE-trending Tangwu-Gegou fault and the NW-trending Mengshan fault. Covered by the Cenozoic sediments, the boundaries of main tectonic units in the study area are almost all concealed, and it is necessary to further investigate the change in the strike of the eastern end of the Mengshan fault as well as the distribution of the angular unconformity along the northern boundary of the Linyi uplift. Using the latest 1:50,000 high-precision gravity data, this study mainly investigated the positions and intersection relationships of the boundaries of tectonic units based on the qualitative analysis of gravity field, the interpretation of multiple gravity potential field conversion, and the division scheme of geotectonic units in Shandong Province. The analysis results are as follows. The Mengshan fault at the junction of the Mengshan uplift and the Pingyi sag transitions from the NW trending to nearly-EW trending in the east of Bancheng Town, significantly cuts the NE-trending Tangwu-Gegou fault, and shows a NW-trending turn to the east again. The angular unconformity at the junction of the Linyi uplift and the Pingyi sag neither ends in the Mengshan fault in the north nor turns southward but extends to the Tangwu-Gegou fault in the east. This unconformity also controls the southern boundary of the Pingyi sag, making the NW-trending banded gravity anomalies of the sag turn eastward. Consequently, the boot-shaped low-value gravity anomalies were formed in the study area. Based on the high-precision gravity boundary identification, this study determined the fault system and tectonic division of the northeastern margin of the Linyi uplift, providing high-precision gravity data for the basic geological study in the study area and laying a good foundation for further mineral geological survey.

Many karst fracture-vug reservoirs have been found in the Ordovician carbonate paleo-buried hills in the Lungu area,Tarim Basin.Hydrocarbons are mainly enriched in these fracture-vug reservoirs,which are mainly related to the paleo-underground river system in carbonate paleo-buried hills.The paleo-underground river system is well developed,especially in the western Lungu area.The fracture-vug reservoirs related to the paleo-underground river system have strong longitudinal and lateral heterogeneity,and ascertaining the seismic and geological characteristics of the paleo-underground river system in this area is the key to the efficient development of fracture-vug reservoirs in this area.Based on the characteristics of modern karst underground rivers and the log and drilling data of this area,this study established a geological model of underground rivers for forward modeling.The study results are as follows.The underground river system developing under the tight limestone setting showed continuously linear strong reflections on the seismic profile.The seismic amplitude decreased as the height and width of underground rivers decreased,and higher seismic amplitude corresponded to larger underground river caves and lower filling velocity.The amplitude can accurately characterize the horizontal range of the underground river on the seismic profile.Meanwhile,the frequency and phase can describe the outline of the underground river on the seismic profile,but the outline described was larger than that of the real underground river.The main channels of the underground river system were prone to be filled with mud.By contrast,the branch channels had a low filling probability and thus serve as the main areas for both the occurrence of underground river reservoirs and the hydrocarbon accumulation.

The Daguanchang uranium deposit, a typical concealed volcanic hydrothermal uranium deposit, was selected to investigate the relationship between surface geochemical characteristics and deep uranium ore bodies of volcanic hydrothermal uranium deposits in North China. The samples for soil survey were collected in the Daguanchang mining area. They were taken from the soil in the upper part of boreholes revealing deposits and mineralization for the analyses of the instantaneous radon (Rn) concentration, mobile-state uranium, and ²¹⁰Po of soil. Then, this study explored the relationships between these geochemical characteristics and deep uranium ore bodies. The results are as follows. The soil in the upper part of boreholes revealing high-grade deposits (also referred to as high-grade boreholes) had significantly higher instantaneous Rn concentration than that in the upper part of boreholes revealing mineralization (also referred to as mineralization boreholes). The high instantaneous Rn concentration in the soil samples collected from a large area corresponded well to the deep uranium ore bodies. The high-grade boreholes had slightly high ²¹⁰Po. However, the ²¹⁰Po in the surface soil samples showed small dispersion and relatively uniform distribution and did not exhibit differences between the barren and mining areas. Mobile-state uranium in high-grade boreholes did not exhibit significant anomalies. The maximum anomaly value of mobile-state uranium in soil samples collected from a large area occurred in the known barren areas. Therefore, it can be preliminarily concluded that, for the exploration of deeply buried uranium ore bodies on a large scale, the anomalies of instantaneous Rn concentration in the soil can indicate the anomalies of deeply buried uranium ore bodies, while the mobile-state uranium and ²¹⁰Po in soil are less sensitive than instantaneous Rn.

The Matou gold deposit is located in the Mianning-Yanyuan strike-slip orogenic belt and is part of the deeply cut Quaternary coverage area and, thus, has limited surface prospecting clues. In this prospecting stage, a comprehensive anomaly area was delineated through the 1:10 000 soil geochemical survey. Then, gold ore bodies were discovered through trenching engineering, indicating excellent prospecting performance. Moreover, this study established a geological-geochemical prospecting model dominated by the HT³ anomaly area by combining the geological and geochemical anomalies in the work area. Finally, the next prospecting direction was proposed.

This study explored the geothermal resources in Yueliangwan, Binhai County, Jiangsu Province using the controlled source audio-frequency magnetotellurics (CSAMT) method and the wide-field electromagnetic method. Through the auxiliary correction of near-field and transition-field curves, as well as the inversion based on the CSAMT data, this study obtained the electrical structure information of underground geothermal resources in the Binhai port. Meanwhile, this study acquired the information on the underground geometric structure using the microtremor exploration method. By comprehensively analyzing the interpretation results of three kinds of geophysical data, this study obtained the geothermal model of the study area and determined the locations of the anomalies. A geothermal well with a depth of 2 919 m was drilled in the study area, obtaining water yield of 2 171 m³/d with a water temperature of 51 ℃. The high consistency between the results from the comprehensive geophysical exploration and the geological and geothermal well data indicates that the comprehensive geophysical exploration method can improve the reliability of geothermal exploration results.

The Nanjinshan gold deposit is a typical epithermal deposit in Beishan metallogenic belt, which extends in a N-E direction to the peripheral shallow cover zone. In order to further achieve the breakthrough of prospecting in the peripheral shallow overburden area, the pilot work of motorized shallow drilling geochemical survey carried out. Based on the nature and thickness of the overburden, 126 motorized shallow drilling geochemical exploration samples are taken in the shallow overburden area using the vehicle mounted air positive circulation and three wing alloy scraper drilling or pneumatic DTH hammer drilling technology, with a sampling density of 16.8 points per square kilometer. The shallow drilling geochemical exploration methods and technologies in the shallow overburden area are further discussed, including the selection of drilling technology, sampling network, sampling materials, sample collection, etc. Soil survey was carried out in sporadic bedrock areas, and 278 samples were collected, and the sampling density was 48.77 points per square kilometer. Fifteen elements including Au, Ag, as, Sb, Hg, Cu, Pb, Zn, W, Sn, Mo, Bi, Cr, Co and Ni were analyzed. Through the above work, seven comprehensive geochemical anomalies were delineated. After anomaly investigation, six gold deposit bodies and one silver deposit body were found in the new circle in the bedrock area, and two concealed gold deposits and one silver deposit body were found in the shallow overburden area. The results show that shallow drilling geochemical survey is effective and feasible in the shallow overburden area of arid Gobi landscape in Beishan.

The Dongjianian silver deposit, located on the southern margin of the Xiaoqinling Mountains, is controlled by the secondary structures of the Xiaohe fault and is the first large precious metal deposit discovered in the southern belt of the Xiaoqinling Mountains. This deposit has three hydrothermal metallogenic stages, namely the quartz-pyrite metallogenic stage (Ⅰ), the dominant quartz-polymetallic sulfide metallogenic stage (Ⅱ), and the quartz-carbonate metallogenic stage (Ⅲ). Three types of inclusions have primarily developed in the ore bodies, namely gas-liquid two-phase inclusions (W-type), CO₂-bearing inclusions (C-type), and pure CO₂ inclusions (PC-type). Stage I primarily witnessed the development of C- and W-type inclusions and a small quantity of PC-type inclusions, and stage II mainly saw the development of W-type inclusions and a small amount of C-type inclusions. The quartz fluid inclusions formed in stages I and II have homogenization temperature ranges of 151~270 ℃ and 126~240 ℃, respectively, which exhibits a downward trend. Their salinity varies slightly in the ranges of 3.8%~22.42% NaCleqv and 4.16%~20.48% NaCleqv, respectively, indicating a low-salinity environment. Their CO₂ content transformed from enrichment into deficiency. The metallogenic pressure and depth were estimated to be 22.08~76.6 MPa and 3.77~7.13 km, respectively. Therefore, the Dongjianian silver deposit is a low-salinity medium- to low-temperature meso-epithermal silver deposit.

This study extracted 59238 pieces of original data on different scales (1:50000 stream sediment surveys and 1:25000 geochemical surveys) of the middle section of the northern margin of the Qaidam Basin. Based on these data, this study conducted the superposition analysis of mathematical index statistics and multivariate statistics, aiming to discover the element association relationship and determine the major metallogenic elements in the region and provide basic support for subsequent mineral work. According to the statistics, the mathematical indexes of Au, W, and Cr in the study area show great metallogenic potential. Combined with the multivariate statistical analysis and existent metallogenic facts, the authors of this study believed that the study area has the great potential for the prospecting of chromium deposits associated with ultramafic rocks besides tectonic altered rock-type and hydrothermal gold deposits. Owing to the relatively high overall background value of local chromium (Cr) element, the traditional method using X+2σ (129×10^-6) or the cumulative frequency 85% (142.9×10^-6) used to delineate the anomaly threshold cannot meet the requirement for delineating local anomalies in the study area. Therefore, this study improved the anomaly threshold using the 1/4 concentration grading value (234×10^-6). As a result, many anomalies exhibiting significant zonal distribution in the concentration center were delineated, and most weak anomalies were eliminated. Based on the geological, geophysical, and geochemical results, this study inferred zones favorable for the further exploration of chromium deposits and determined four favorable metallogenic zones and five prospecting areas.

In coal mining, the accurate determination of the locations of the footwalls and roofs of coal seams and the identification of the geological structures that threaten the safety of excavation are important measures to ensure safe coal mining. This study proposed a technique for detecting the footwalls and roofs of coal seams, which consisted of a mining face-based borehole radar detection method for underground coal mines and a data processing process. Then, this study applied this technique to the Xinyuan coal mine. Specifically, radar profiles were denoised and enhanced through the correction of zero-moment point, DC elimination, band-pass filtering, direct wave removal, and gain processing of measured borehole radar data of boreholes along a mining face of the Xinyuan coal mine. Then, the locations of the roofs and footwalls of coal seams in the underground coal mines were identified and presented through a series of processing and interpretation, including velocity pickup, reflective surface extraction, and diffraction stack migration, as well as time-depth conversion, flipping, splicing, and the correction of borehole trajectories. The technique proposed in this study serves as an effective means for the safe operation of coal mines and thus is of value for promotion.

Echoes can be distorted due to the temperature drift of the ground penetrating radar (GPR) system,the low-pass effect of lossy media,and the decline in the coupling between the antenna and the ground.The mixing of effective radar echoes and zero-offset components makes it difficult to detect weak signals.The conventional front-end correction and post-processing methods,which aim to improve the transmission efficiency and remove the clutter noise,fail to improve the signal-to-noise ratio (SNR) and sensitivity of the system.To overcome these obstacles,this study improved the equivalent sampling circuit using a real-time correction method based on time-varying zero offset.Specifically,the zero-offset coefficient of each sampling was controlled separately and was updated in real time on each sampling.No DC and low-frequency components were sent into the subsequent programmable amplifier along with effective signals,ensuring the correct acquisition of weak signals and the dynamic range of the system.Experiments have proved the validity and feasibility of this method,which has been applied to a new type of digital GPR product.

With the intensification of hydrocarbon exploration in ultradeep reservoirs, conventional seismic exploration methods are no longer applicable to areas with complex surface structures and underground geological structures because they are difficult to acquire effective reflection information with high signal-to-noise ratio, the imaging effects of seismic data are poor, seismic profiles fail to clearly present the geological structures of study areas. Based on the large-scale low-frequency vibroseis excitation technology, the field acquisition requirements, and geological tasks, this study adopted a high-density two-dimensional wide-angle reflection seismic observation system to collect seismic data. This study selected the optimal field acquisition parameters suitable for the study area through numerical simulation of wide-angle seismic waves and field tests. As indicated by the results of this study, the wide-angle reflection acquisition technology for ultradeep reservoirs based on large-scale low-frequency vibroseis can acquire weakly reflected seismic signals at locations with far offset and strong energy, especially the deep low-frequency information, thus effectively improving the signal-to-noise ratio of seismic data. Compared with conventional seismic stacked sections, the wide-angle reflection seismic stacked sections have significantly improved quality, continuous events, clearly visible structural parts, and encouraging seismic imaging effects. The field production practices dominate that the wide-angle reflection seismic exploration technology can be applied to ultradeep hydrocarbon exploration.

The seismic forward modeling technique is critical to seismic exploration.Moreover,it shows a faster rate and higher calculation efficiency in the frequency domain than in the time domain.Presently,there is a need to complete the forward calculation in the frequency domain efficiently and accurately.The specific problems include the numerical dispersion and the high memory consumption for calculating and decomposing impedance,which should be reduced by improving the calculation efficiency.Different from the conventional direct method,this study adopted the least-squares conjugate gradient (LSCG) method used to determine the impedance matrix for the frequency-domain forward modeling and proposed an expression for wavenumber compensation to suppress the numerical dispersion.The numerical tests of simple and complex models show that the LSCG method can effectively reduce the calculation time and that the frequency-domain forward modeling method based on wavenumber compensation can effectively suppress the numerical dispersion and thus improve the precision of wave field simulation.

The lack of low-frequency data in actual seismic data makes the full waveform inversion (FWI) tend to fall into the local minimum,resulting in poor inversion quality and unreliable results.In view of this,data-driven low-frequency recovery mapping was adopted in this study.First,high-pass and low-pass filters were employed to separate high-frequency and low-frequency data from raw data,respectively,and then data preprocessing was carried out.The processed data were used as the training set of the model.Then,the model was built based on the U-Net to establish the mapping relationship between high and low frequencies.To effectively prevent the model from overfitting,the dropout layer and batch processing layer were added based on the U-Net model.Finally,the trained model was used to predict the corresponding low-frequency data from the high-frequency data and conduct inverse data preprocessing.The errors between the predicted low-frequency data after inverse data preprocessing and the real low-frequency data were compared and analyzed,The effectiveness of multi-scale FWI was verified using the depression and Marmousi models.The experimental results show that the average relative errors between the predicted low-frequency data and the real low-frequency data were 5.02% and 13.32%,respectively for training and test data,indicating small errors and high data coincidence.The inversion results of the depression model,the Marmousi model,and actual data show that the prediction of low-frequency data significantly improved the inversion quality and delivered a great performance in the processing of data with much noise.

Aiming at the ill-conditioned coefficients in the traditional carrier magnetic compensation, this study investigated the main source of magnetic interference, simplified the original model by ignoring the influence of the eddy current field, and established a three-component magnetic compensation model. Accordingly, it proposed an online carrier magnetic compensation method for the magnetic field components. Compared with the traditional method, the method proposed in this study effectively improved the compensation accuracy by about 1.14 nT. This study conducted embedded hardware simulations of this method using the high-level synthesis (HLS) tool of the field programmable gate array (FPGA), verifying the real-time performance and magnetic compensation accuracy of this method in a hardware system.

The semi-airborne transient electromagnetic method (SATEM) is an emerging flexible and efficient geophysical exploration method using ground launch and air reception. The present inversion methods applied to the SATEM produce very smooth inversion results since they apply the maximum smoothing criterion, thus failing to effectively identify the information of specific layer interfaces. This study introduced the focusing inversion theory to the one-dimensional inversion of the SATEM. First, a focusing inversion stabilizer was determined by selecting appropriate focusing and regularization factors. Then, the inversion objective function including the focusing inversion stabilizer was solved to allow the inversion results to effectively identify the abrupt interfaces of layered strata. Furthermore, multiple layered geoelectric models were built to verify the reliability of the focusing inversion. Moreover, the focusing inversion results were compared with the Occam inversion results to highlight the advantages of the focusing inversion in interface identification. This study conducted the focusing inversion calculation of actual data on groundwater detection of a certain area. The calculation results were then combined with the hydrogeological and logging data for comprehensive analysis. Finally, this study determined the locations and spatial distribution of underground aquifers in the area, verifying the feasibility of the SATEM for groundwater detection.

The channel sand reservoirs in the Longfengshan area have the characteristics of typical lithologic reservoirs.This area has thin sand bodies,narrow channels,and strong vertical and horizontal lithologic heterogeneity.It is difficult to predict the reservoirs at a depth of 5 m or greater.The frequency-divided iterative inversion can fully utilize the full-frequency band seismic data and transmit the seismic information of different frequency bands and scales step by step,thus optimizing the inversion results.In this study,the seismic signal frequency bands were divided using the matching pursuit algorithm to obtain seismic data volumes of different scales.Under the constraints of log data,the low-frequency,large-scale inversion results were used as the initial model for the next-order frequency band inversion,and the inversion results.During the inversion,wavelets were adaptively selected using the correlation algorithm to enhance the inversion accuracy.Regularization parameters were adaptively selected based on the Bayesian theory to adjust the relationship between resolution and stability to achieve the optimal balance and avoid chaos in inversion.In 2019,gas reservoirs in subzones 1-2-6 and 1-2-8 of the Yingcheng Formation were encountered in the drilling of four wells in the Longfengshan area.This result is consistent with the inversion prediction results.Therefore,compared with conventional frequency division inversion,the method proposed in this study has the advantages of high inversion accuracy,coincidence with seismic information,and full application of frequency bands.This method can effectively improve the identification performance of thinly laminated channel sand bodies and guide the exploration and development of related lithologic reservoirs.

Based on spectral inversion,this study proposed a p-wave impedance inversion algorithm for post-stack seismic data to improve inversion accuracy.Spectral inversion is widely used in high-resolution seismic inversion and the reflection coefficient inversion.Based on the odd-even decomposition of reflection coefficients,spectral inversion can reduce the tuning effect between thin layers and enhance the resolution of inverted data volumes.However,the calculation of p-wave impedance using reflection coefficients is ill-posed, and the step-by-step inversion of p-wave impedance tends to introduce a large cumulative error.Therefore,this study proposed a post-stack p-wave impedance inversion method based on spectral inversion.This method introduced the objective equation constrained by TV regularization and calculated the relative p-wave impedance using the iterative method.Then,the absolute p-wave impedance was determined through the frequency-domain fusion of the relative p-wave impedance and the pre-built low-frequency model.As demonstrated by the model and actual data,the method proposed in this study has a higher inversion resolution than the impedance inversion based on sparse-spike deconvolution and is more conducive to subsequent research such as reservoir prediction.

The conventional spectral bluing technique is mainly utilized for post-stack seismic frequency expansion.It is applicable to the shallow strata where sandstones and mudstones can be effectively identified based on the wave impedance of logs.However,this technique has many limitations for the impedance aliasing zones of moderately deep strata.The amplitude versus offset (AVO) gradient reflects the change in the relative reflection coefficient with offset and is positively correlated with the rate of change in Poisson's ratio,which can distinguish between sandstones and mudstones in moderately deep strata.Through forward modeling,this study first proved the reliability and stability of the AVO gradient in identifying the top interface of sandstones in moderately deep strata according to the changes in parameters such as lithologic association,physical properties,and fluids.Furthermore,to improve the characterization precision of thin sandstone interbeds in moderately deep strata,this study proposed a AVO gradient-based spectral bluing for seismic frequency expansion.The model tests and practical applications show that the spectral bluing based on AVO gradient can directly identify the information on reservoir interfaces and simplify the multi-parameter lithology prediction method based on CRP gathers or partial angle stack data.Moreover,the new technique proposed in this study can effectively characterize the thin sandstones in deeply buried strata in the XH sag and provides a reference for high-resolution seismic processing of moderately deep strata.

Large-scale mining activities have been continued in key exploration areas. Consequently, the mined-out areas, waste dumps, and tailings ponds of mines are constantly deforming. As a result, the digital terrain method fails to make the terrain data closely match the airborne gravimetric data, leading to serious correction errors in airborne gravity terrain correction and stone-slab correction. This study calculated the difference between the GNSS geodetic height and the radio terrain clearance altitude of the helicopter gravity and magnetic survey system and then converted the GNSS geodetic height into normal height. Then, the synchronous surveyed terrains were obtained through leveling and fine-scale processing. Moreover, the surveyed terrain data, together with various collected terrain data, were compared with the ICESat-2/ATL08 spaceborne laser elevation. The results show that the surveyed terrains Wxd100 and Wxd400 had elevation precision of 5.33 m and 8.93 m, respectively. After airborne Bouguer gravity correction was conducted using the surveyed terrains, the data quality of the mining area and several typical survey lines was greatly improved.

The soil cation exchange capacity (CEC) refers to the total amount of various cations that can be absorbed by soil colloids. It is an important measure of the buffering capacity and fertilizer retention capacity of soil and is also an indicator that must be analyzed in soil environment assessment. The conventional ammonium acetate exchange method described in Chinese forestry standard LY/T 1243—1999 has been widely used in soil and agrochemical laboratories in China due to its high stability, buffering capacity, and repeatability. However, when applied to the batch analysis of soil, this conventional method is time-consuming and has other shortcomings such as cumbersome steps and low efficiency. Based on previous studies, this study optimized the conventional ammonium acetate exchange method in three steps, namely centrifugation, distillation, and titration. Specifically, samples were treated with displacement using mixed EDTA and ammonium acetate solution and cleaning with ethanol using the CEC pretreatment system. Then, the ammonium ions displaced were determined using an automatic Kjeldahl apparatus, followed by the calculation of the CEC. This study discussed the effects of the stirring time of ammonium acetate, ethanol dosage, and distillation time in the Kjeldahl apparatus on CEC determined. On this basis, this study comprehensively established and optimized the method for determining the CEC in soil using the CEC pretreatment system and the Kjeldahl apparatus. As shown by the experimental results, under the optimal conditions of displacement time, ethanol dosage, and distillation time, the optimized method determined the CEC of a batch of samples (100) in only 8 h, which was shortened by nearly 85% compared with the conventional method, thus greatly improving the efficiency. As verified using the certified reference material for the chemical composition of first-grade soil, the determined CEC values agreed with the certified values, with relative standard deviations (n = 6) of all less than 2%. The optimized method is characterized by high efficiency and simple operation and can greatly reduce possible errors caused by manual operation and improve the accuracy of results. Therefore, it is applicable to the bulk determination of soil CEC.

Geomagnetic field surveys have been widely applied in the fields such as basic geological study, mineral resource exploration, and military detection. A key tool for geomagnetic field surveys is helium optically pumped magnetometer probes. The frequency modulation precision of the radio frequency field used in the probes is an important factor affecting geomagnetic survey precision. To achieve frequency modulation signals featuring easy modulation, high precision, and high reliability, this study proposed an intelligent frequency modulation technology for the radio frequency field of the magnetometer probes by combining the direct digital frequency synthesizer (DDS) and the microcontroller unit (MCU). This technology can achieve flexible, real-time, automatic, and precise frequency modulation of the radio frequency field of the magnetometer probes. As revealed by the integration tests in which frequency modulation signals were loaded into the helium optically pumped magnetometer system, the magnetometer can obtain stable and precise magnetic resonance signals, thus ensuring high-precision geomagnetic field surveys.

As shown by the investigation and analysis of the Se content in soils and rocks of the Xining Basin, the rocks and soils in the Paleogene Xining Formation and the Cretaceous Minhe Formation have the highest Se content, which makes them the major Se-rich parent materials of soils in the basin. By combining the paleogeographic data on the retreating process of the basin, it can be concluded that the Paleogene Xining Formation and the Neogene Guide Group were deposited from the arid and hot saline lacustrine facies to the humid and cool saline-freshwater lacustrine facies. The combined action of the saline lake boundary and the arid and hot saline-lacustrine environment, as well as the following transformation by landforms and water systems, contributed to the formation of the existing framework of saline-lacustrine sedimentary Se-rich soils in the Xining Basin. Such Se-rich soils enjoy the advantages of a low heavy metal content, a moderate Se content, and a high available Se content and thus are of great value in development and utilization.

This study investigated the speciation of selenium in 51 surface soil samples from the selenium-rich cultivated land in Linhe District, Bayannur City, Inner Mongolia and explored the content and speciation of selenium and their influencing factors. The results showed that the surface soil in the study area had total selenium content of (0.19~0.48)×10^-6, averaging 0.33×10^-6, indicating a soil environment with moderate-high selenium content. Among the seven forms of selenium speciation, major forms include the residue, humic acid bound, and strong organic bound forms. The remaining forms, namely water-soluble, ion exchange, iron-manganese oxide bound, and carbonate bound forms accounted for only 13.67%. Water-soluble selenium consisted mainly of moderate-high water-soluble selenium (92.16%), with the absence of water-soluble selenium deficiency. The selenium content in each form was highly correlated with the total selenium content in the soil. The organic matter content, pH, Eh, and CEC had different effects on the distribution characteristics of selenium speciation.

Land is an important basic resource for human survival and stable social and economic development, and cultivated land is an integral part of land resources. Ascertaining the quality of cultivated land is of great significance for the scientific and rational utilization of cultivated land and the sustainable development of green ecological agriculture. Using the methods for 1:50,000 geochemical survey and evaluation, this study conducted the quality evaluation and the classification of land in the study area based on the contents of beneficial nutrient elements and toxic and harmful elements in soils and analyzed the distribution and controlling factors of elements in soils. The results of this study are as follows. The soils in the study area consist mainly of alluvial-proluvial deposits from the Yellow River and are primarily used for agriculture and animal husbandry. The soils are not contaminated by heavy metals and are rich in nutrients, with the first- and second-grade excellent soils collectively accounting for 88.85%. Moreover, most soils in the study area have moderate selenium content. Therefore, it is recommended that selenium-rich land resources should be incorporated into the government land planning to develop agriculture with distinctive local features.

This study investigated the distribution characteristics of saline groundwater in the Huimin area of the lower reaches of the Yellow River using the DC resistivity method. Specifically, this study determined the distribution range of the apparent resistivity of the saline water and the variation in the saline-fresh groundwater interface in the area based on resistivity logs, aiming to constrain the resistivity sounding data analysis and improve the interpretation accuracy of the distribution of the saline groundwater. The results are as follows. The top boundary of the saline water in the area mainly had a burial depth of 20~50 m and developed to the shallow surface locally. It was inferred that the bottom boundary of the saline water had a burial of mainly 160~300 m and gradually became shallow in a nearly NW direction. As verified by the later investigation of water samples and drilling, the inferred saline groundwater characteristics agreed roughly with the actual situation. This result indicates that the DC resistivity method has a good application performance in the study of the distribution of saline groundwater.

Determining the boundary between shallow saline water and freshwater in areas containing (brackish) saline water can guide the exploitation and utilization of local shallow water resources. This study analyzed the characteristics of underground shallow electrical structure through inversion based on the frequency-domain airborne electromagnetic data. Then, it inferred the boundary between the shallow (brackish) saline water and freshwater in the study area. By comparison with the boundaries between saline water and freshwater obtained from two hydrological surveys in 1998 and 1999 and by combining the surface hydrogeological data, this study revealed that the shallow groundwater cones of depression affect saline water intrusion trends in the Xiong’an New Area, and the details are as follows: The (brackish) saline water intrusion in the Zangang-Mijiawu-Shuangtang area in the northeast of Xiongxian County tends to be stable due to the presence of the Zangang groundwater cone of depression. However, this cone has also intensified the (brackish) saline water intrusion in southern Zangang Town. Compared to 1999, the (brackish) saline water range on the west side of Anxin County has continuously decreased due to the rise in the water level of the Rongcheng groundwater cone of depression. The continuous decrease in the water level of the Gaoyang groundwater cone of depression determines that the (brackish) saline water range in the Luzhuang-Gaoyang direction will continuously expand. These predicted (brackish) saline water intrusion trends will provide data support for the rational exploitation and utilization of water resources in the construction of the Xiong'an New Area.

Magmatic rock areas suffer poor water yield property and lack groundwater overall, encounter great difficulties with water exploration, and generally face the problem that available water resources fail to meet the demand. Targeting different types of water exploration targets and combining the geological and physical property characteristics, hydrogeological conditions, and field survey of the exploration target areas, this study comprehensively analyzed the electric structure characteristics, well completion modes, and water yield mechanisms of the strata around Xiaoshuicha and Wawu villages in Laiyang City through interpretation and analysis using comprehensive geophysical exploration method consisting of apparent resistivity profiles and apparent resistivity-based vertical sounding. After determining water exploration targets, conducting interpretation and analysis of geophysical prospecting, and locating wells through comprehensive analysis, this study successfully drilled two wells in the two villages, obtaining maximum water yield of 247.56 m³/d and 620.64 m³/d each. Finally, this study analyzed the water yield mechanisms in detail based on the intrusion-contact zone types and water-storage structural models with dykes conducting water. This study not only solves the difficulty with water use of local people but also provides a certain reference for future water exploration and well locating in similar areas.

The detection of landslide deposits is frequently required in the infrastructure construction of the Western China Development. However, it is difficult to distinguish the landslide deposits using conventional electromagnetic methods because of the small differences in the resistivity between the sliding surface of the sliding bed and the Quaternary overburden. Therefore, this study proposed a scheme that detected the landslide deposits using opposing-coils transient electromagnetics (OCTEM) and then traced the mountain dislocation surface reversely. Accordingly, this study established a geoelectric structure model of the landslide deposits, investigated the transient electromagnetic response patterns of landslide deposits through forward calculation, and theoretically analyzed the transient electromagnetic response patterns of landslide deposits with different thicknesses and those of landslide deposits under different thicknesses of the Quaternary overburden. As verified by the detection results of known landslides, the method proposed in this study is correct and that OCTEM is valid in detecting landslide deposits in mountainous areas.

In recent years,surface karst collapse has frequently occurred in Beihuan New Village,Guigang City,Guangxi,severely threatening the life and property safety of local residents.This study analyzed the distribution of karst in the study area using electrical resistivity tomography (ERT) and delineated zones with strong groundwater runoff,aiming to guide the prevention and control of karst collapse.First,this study conducted numerical simulations to guide the preparation of the field exploration scheme and provide a reference for the analysis of the results measured in the field.Then,it explored the zones with shallow groundwater runoff in Beihuan New Village,delineating 11 zones with potential karst collapse and inferring one major runoff zone and three minor runoff zones.Finally,this study compared the exploration profiles with borehole logs.The comparison and verification results show that ERT has high precision and reliability and can play a significant role in the exploration of urban surface karst collapse.

The Dashui gold deposit in Maqu County,Gansu Province is a typical mine of the western Qinling region.Owing to continuous mining,many mined-out areas have been formed at different depths below high and steep slopes No.5 and 9,causing local surface collapse and major safety hazards.According to the requirements for environmental protection and safety,there is an urgent need to determine the spatial distribution of concealed collapse to effectively prevent geological disasters.Using the opposing coils transient electromagnetic method (OCTEM),this study conducted the fine-scale interpretation of the anomalies on the typical sections of the exploration area.Based on this,as well as the comprehensive analysis of the hydrogeological data and basic geological data of the exploration area,this study determined the transparent and three-dimensional distribution of the concealed collapse of the Dashui gold deposit.The results of this study show that the subsurface investigation of mined-out areas using the OCTEM can effectively reveal the lithologic and electrical characteristics of concealed strata in mined-out areas.Moreover,the significantly different physical properties between mined-out areas and surrounding rocks can be used to effectively identify the locations and basic morphologies of subsurface mined-out areas.The data on the boundary characteristic points of the mined-out areas on geophysical profiles with multiple exploration lines and three-dimensional modeling allow for the three-dimensional visualization of the spatial morphology of the mined-out areas.The application performance of the OCTEM,along with three-dimensional modeling,provides a technical basis for mine restoration and safety evaluation,thus effectively serving the construction of digital mines.