Ji'nan possesses highly abundant geothermal resources, which are hosted by Ordovician-Cambrian karst-fissured geothermal reservoirs and Neogene-Paleogene clastic pore-fissure geothermal reservoirs. The geothermal exploration in this study focuses on the Ordovician-Cambrian karst fissured geothermal reservoirs in Daqiao Town in northern Ji'nan. Through geophysical profile measurements, this study aims to identify the distributions of strata and fault structures and the burial depths of geothermal reservoirs, infer the attitudes and spatial morphologies of fault structures associated with heat control and conduction, delineate the target area for geothermal well construction, and conduct drilling verification in the favorable underground water-rich position. Building on the collected data, this study interpreted and inferred the fault structures in the study area and comparatively analyzed the water-bearing properties by employing direct-current sounding, controlled source audio magnetotellurics, and magnetotelluric survey. A geothermal exploration and production combined well was constructed in a favorable position of the geothermal target area, manifesting a completion depth of 1 532.06 m, a static-water burial depth of 13.03 m, a wellhead water temperature of 50.1 ℃, a water yield of 132.998 m³/h, and a dropdown depth of 18.27 m.

Following China's planning for ore prospecting in overburden areas, China's geochemical exploration researchers have conducted extensive research on the fundamental theories, methods, and technologies of geochemical exploration for overburden areas in the past decade. They achieved significant advances mainly in two aspects: (1) the research on the migration mechanism, occurrence state, and anomaly formation mechanism of elements in overburden areas; (2) advances in methods and technologies, including geoelectrochemistry, active state of elements, geogas, separation of micro-fine-sized soil particles, soil thermomagnetic composition, and integrated gas survey, as well as numerous experimental demonstrations. These advances represent continuous progress in the research on the fundamental theories, methods, and technologies of geochemical exploration for overburden areas, providing new geochemical methods and technologies for ore prospecting breakthroughs in overburden areas.

The Laiwu area in central Shandong Province, situated in the eastern North China Craton, is a significant production area of skarn iron-rich ores. Its ore deposits occur primarily in the contact zone between the mining rock mass and the Middle Ordovician carbonate formation. Based on the latest areal gravity and magnetic survey results, this study thoroughly investigated the characteristics of gravity and magnetic anomalies along the Shijiaquan-Liujiamiao area in the western periphery of the mine rock mass. Then, this study delineated the deep prospecting target combining the characteristics of gravity and magnetic fields of the known iron deposits in the Laiwu area. Large-scale gravity and magnetic profiles were arranged in the favorable mineralization area. With the known boreholes as constraints, the gravity and magnetic anomalies were qualitatively and quantitatively interpreted using the 2.5D gravity-magnetic joint inversion technique. The interpretation results provide a basis for the location and depth of the borehole to be placed, which revealed a 15.8 m-thick iron-rich ore deposit, suggesting remarkable prospecting effects. This study holds critical indicative significance for further exploration of skarn iron ore deposits in this area.

Despite abundant geothermal reserves of the Tangyu geothermal field in Meixian County, Shaanxi Province, long-term exploitation has decreased the water temperatures and yields of its existing geothermal wells year by year. Hence, there is an urgent need to explore new potential geothermal resources in the geothermal field. Since the known geothermal wells in the geothermal field are significantly controlled by faults, investigating the deep fault propagation holds critical significance for exploring the geothermal field’s potential geothermal resources. Due to the method limitations and the topographic influence, identifying thermal control faults through conventional geological route investigation or large-scale engineering is not applicable to the geothermal field. Therefore, a new technical method combining the penetrating soil radon measurement and the controlled source audio magnetotelluric (CSAMT) method was employed in this study to find concealed faults and delineate potential geothermal areas. Based on the measured surface soil radon concentration anomaly data and the subsurface electrical structure model derived from the CSAMT data inversion, this study inferred six new concealed faults on the basis of corroborating the known faults, predicted two potential geothermal areas, and built a conceptual model for the Tangyu geothermal field. As revealed by the results, the soil radon concentrations at concealed faults are much higher than the regional background value, and the concealed faults are located in the low-resistivity fracture zones as indicated by the apparent resistivity results based on CSAMT data inversion. Besides, the two potential geothermal areas spread from 450~750 m and 850~1 150 m on the profile, respectively, at depths of approximately 250~300 m. This study concludes that the geothermal field resides in a low-resistivity region with soil radon anomalies three times the regional background value. The results of this study provide a reference for the subsequent sustainable production and utilization of potential geothermal resources in the region.

Geothermal resources are significant clean energy and tourism mineral resources. The Rucheng Basin, a carbonate basin in the southeastern mountainous area of Hunan Province, possesses favorable conditions for the formation of convective geothermal energy. However, the basin is enclosed on three sides by the giant Zhuguangshan rock mass, and its basement is subjected to the intrusion and destruction by the rock mass, resulting in severely deformed formations, crisscrossing faults, and significantly different eastern and western structures. The understanding of the basin's water- and heat-conducting pathways and deep reservoir structures remains elusive, thus restricting the investigation of the basin's geothermal potential. Hence, this study probed the basin's deep structures through gravity survey and audio magnetotellurics (AMT), obtaining the following insights: (1) The Rucheng Basin has developed into a bidirectional ramp structure due to east-west differentiation. The synclinorium in the east experienced compression and clockwise rotation due to the emplacement of the Yanshanian rock mass, rocks were fragmented in the core zone, and strike-slip fracture zones were found at the boundary. The faults have vertical cutting depths exceeding 4 km, widths ranging from 300~600 m, and dip angles between 80°~90°. (2) The basin's basement anticlinal axis hosts several NWW-directed concealed rock masses, with diameters from 3~4 km and buried depths from 0.5~1.5 km. Hot springs reside in the fracture zones crossing the boundaries of the concealed rock masses. (3) The basin boasts favorable conditions for the formation of convective geothermal energy. Folds, fault zones, and concealed rock masses match each other to form a unified spatial combination of heat-controlling elements, manifesting heat accumulation characterized by east-west recharge and intermediate discharge. With more thriving deep geothermal reservoirs in the east, the basin has high potential for geothermal resources.

The eastern Kunlun metallogenic belt, as a significant metal metallogenic belt in China, hosts extensive orogenic gold deposits and large-scale Kunlunhe, Gouli, and Wulonggou gold concentration areas. The Dachaigou gold deposit is a large-scale gold deposit newly discovered in the Wulonggou gold field in recent years. Despite its high metallogenic potential, the western extension of its ore belt has not been defined. Hence, this study conducted induced polarization (IP) sounding and wide-field electromagnetic sounding in the deposit. The results show that the known ore belt is situated in the regional gravity anomaly gradient zone, the transition zone of positive and negative weak magnetic anomalies, the edge of IP anomalies, or the electrical gradient zone. The development zone of the regional tectonic belt resides in the large-scale IP anomaly section. The regional tectonic belt is characterized by a wide range of low-resistivity anomaly zones. The IV and III alteration zones of the known ore belt are located in the opening position of the low-resistivity anomaly zone and the shallow electrical anomaly gradient zone, respectively. Based on the above understanding and the electromagnetic anomaly change patterns of several parallel profiles in the western extension segment, it was inferred that the regional ore-controlling structure extends steadily in the W-NWW direction, forming a favorable prospecting space in the western extension segment of the deposit. The results of deep geophysical exploration in the Dachaigou deposit indicate that geophysical methods manifest significant advantages in deep geological prospecting research, providing successful experience for deep prospecting in the eastern Kunlun gold deposit area.

The Fengtai ore concentration area is an important producing area of plumbum-zinc and gold ores in the middle of the Qinling orogenic belt. It hosts many large to super-large deposits, such as Qiandongshan-Dongtangzi, Bafangshan-Erlihe, Baguamiao, and Shuangwang deposits. With the exploitation proceeding, the reserves of these deposits have decreased significantly, and the ore prospecting in these deposits has shifted from the surface to the deep part. However, the geophysical fields in the deposits are yet to be ascertained, severely restricting research on the metallogenic regularity of the deposits and the ore prospecting and exploration in the peripheral zones. Based on the latest 1∶50,000 aeromagnetic and airborne radioactivity survey data, as well as gravity data, this study investigated the multi-source geophysical fields on the scales of the region, the ore concentration area, and deposits, aiming to summarize the distribution patterns of geophysical anomalies of different scales and provide evidence for research on metallogenic regularity and prospecting prediction. The results show that the Fengtai and the Xicheng ore concentration areas, with similar magnetic structures, are separated by the zone with strong magnetic anomalies caused by the crystalline basement of the Huicheng Basin. The first vertical derivative of gravity reveals that the Fengtai and Xicheng ore concentration areas have density structures similar to the Huicheng Basin. It can be inferred that the shallow part is a unified basin and that a large prospecting space exists between the two ore concentration areas. Many NW-trending linear magnetic anomaly zones occur in the Fengtai ore concentration area. Their locations are highly consistent with those of fault structures, and they were offset by NE-trending structures due to late transformation. The second vertical derivative of gravity reveals that many intermediate-acid intrusive stocks or veins have developed in the deep part of the Fengtai ore concentration area. Structural boundaries can be effectively identified based on the first vertical derivative, X-directional derivative, and wavelet transform of aeromagnetic data. Furthermore, ore bodies are mostly distributed in the NW direction along the tectonic belt. All these will play an important role in guiding ore prospecting and exploration in the Fengtai ore concentration area.

With the rapid development of urban infrastructure,the demand for urban geological work is increasing,and urban geological surveys become particularly important.Urban geophysical exploration has different exploration purposes and working environments from conventional geophysical exploration.Accordingly,compared with conventional geophysical exploration methods,the geophysical exploration methods for urban geological surveys face the challenges of many interference factors,limited construction sites and time,and high requirements for exploration accuracy.The opposing-coils transient electromagnetic(OCTEM) method enjoys a strong anti-interference ability,convenient and efficient construction,and high resolution.Therefore,this study employed the OCTEM method to investigate the test profile in the urban geological survey and evaluation of Haidong City.This test profile was subjected to numerous interference sources since it crossed 11 highways and railways and passed through factories,schools,logistics parks,villages,living quarters,and rivers.Consequently,the OCTEM results agree well with the results of single-point resistivity sounding and drilling results.Therefore,the OCTEM method proposed in this study is effective for urban geological surveys.

The development of Se-rich land has been carried out in many regions of China, achieving remarkable results. However, no Se-rich land or crop has been reported in Tibet. This study analyzed the characteristics and influencing factors of the Se content in the soils and crops of the key arable land areas in Bailang County, Tibet, aiming to lend support to the development and utilization of Se-rich land in the Qinghai-Tibet Plateau. The results are as follows: The soils in the study area have a Se content of (0.05~0.76)×10^-6, which is higher than the background value of soils in Tibet (0.15 ×10^-6); 76.83% of the land in the study area has sufficient Se, and land in the study area with a Se content of greater than 0.3 ×10^-6 covers an area of 45.43 km², as determined according to the standard threshold of Se content in alkaline soils (w(Se)≥0.3 ×10^-6). Further investigation shows that highland barley seeds have a Se content of (0.017~0.17)×10^-6 (average: 0.063 ×10^-6) and rapeseeds have a Se content of (0.043~0.14)×10^-6 (average: 0.078 ×10^-6) in the distribution area of Se-rich soils. As indicated by the root soil results of the zones with Se-rich soils, the Nieru Group controls the source of Se in soils, and Se and effective Se content in the soils are significantly positively correlated with N, P, alkali-hydrolyzable nitrogen, and rapid available phosphorus but is significantly negatively correlated with pH. These results indicate that the behavior of Se is significantly affected by a large number of nutrient elements in the soils and pH. Overall, the distribution areas of Se-rich soils in Bailang County have high soil environmental quality, crops with a high Se content, and great potential for the development of Se-rich plateau characteristic agricultural products.

As a kind of clean energy, geothermal energy has attracted the attention of scholars all over the world in recent years. Previous geochemical exploration methods for geothermal resources are limited to the analysis of individual geochemical indices. Moreover, previous studies of microorganisms in geothermal fields mostly focus on hot spring outcrops, lacking ecological studies of geothermal resources in complex terrains. This study investigated the soil geochemistry and microbial diversity of the Bantang Hot Spring geothermal field in Chaohu, Anhui Province. Geochemical indices such as head-space gas, soil gas, acid-hydrolyzed hydrocarbons, and altered carbonate were detected in this study. Combined with the microbial high-throughput sequencing technology, this study analyzed the composition and spatial-temporal distribution of the microbial population above the geothermal fields in uplifted mountains and the relationship between these bioinformatics characteristics and the geochemical indices. The results indicate that the acid-hydrolyzed hydrocarbons on the surface of the geothermal field showed a maximum methane concentration of 43.7 μL/kg in the area between faults F2 and F3, adequately reflecting the fault location of the geothermal field.Bacillaceae, Hydrogenophilaceae, and Thermodesulfovibrionaceae in the geothermal field and the background area showed large relative abundance differences, which were 0.178%, 0.108%, and 0.060%, respectively. This result indicates that they are sensitive to geothermal resources and correspond well to geochemical indices above the known geothermal field. This study preliminarily investigated the diversity of geothermal microorganisms in the geothermal field and analyzed the corresponding relationships between microbial distribution characteristics and geochemical indexes, providing technical support for the microbiological exploration of geothermal resources.

Xiong'an New Area has great potential for geothermal resources. Carbonate rocks are favorable reservoirs for deep geothermal resources in this area. The integrated geophysical exploration technology is an effective way to ascertain the deep structures and the characteristic stratigraphic structure of carbonate geothermal reservoirs. Aiming at the exploration target of deep carbonate geothermal reservoirs, this study put forward a surface-line-point hierarchical and progressive geophysical exploration model. Using the high-precision gravity and aeromagnetic data, this model first investigated the distribution range of carbonate rocks, the thickness of carbonate strata, the distribution of deep-seated faults, and the fluctuation of bedrocks. Then, it analyzed the low-resistivity anomalies of geothermal reservoir strata using the magnetotelluric method. Finally, this model finely characterized the geothermal reservoir strata using two-dimensional seismic profiles and analyzed the velocity structure and regional structural characteristics of anomaly zones in the geothermal field. Based on the exploration precision and reliability of gravity, aeromagnetic, magnetotelluric, and seismic geophysical methods in the geothermal resource exploration of different stages, as well as other factors such as construction cost and efficiency, this study analyzed the economic applicability of geophysical methods in the exploration of deep karst geothermal reservoirs and suggested that the carbonate geothermal resources should be explored using the geophysical exploration technology combination of gravity, magnetic, and magnetotelluric methods.

Distributed acoustic sensing (DAS) technology, one of the most advanced sound field detection technologies, can achieve distributed, long-distance, and high-precision real-time detection of the ambient vibration and sound field information interacting with optical fiber. The optical fiber exploration system of the DAS technology solves the problems of high cost and deployment difficulty of conventional geophones in complex geological environments. In recent years, the DAS technology has experienced rapid development, especially in monitoring application scenarios that require long-term and large-scale deployment. However, its systematic understanding is insufficient due to divergent research results. To further understand the research advances of the DAS technology in geophysical exploration for more effective subsequent research, this study systematically classified and summarized the development history of the DAS technology and its recent research results in geophysical exploration based on the oil and gas, marine, and environmental engineering application scenarios through literature research. This study focused on the development process of the DAS technology in different directions, the research advances in data processing, and relevant literature with specific results. Finally, this study generalized the development trend and urgent problems of the DAS acquisition system, analyzing the DAS development prospect.

The artificial source electromagnetic method is an important technique for deep resource exploration. The key challenge is to improve the depth and precision of detection through innovative technology. The detection mode of electromagnetic methods is evolving from far-field to near-field, and the study of near-source electromagnetic methods has become an international research frontier in recent years. Building on the recent advancements in wide-field electromagnetic methods and multi-channel transient electromagnetic methods, the short-offset transient electromagnetic method (SOTEM) has been further developed and proposed. The distinguishing features of SOTEM are its stronger signals and wider bandwidth, which are advantageous for achieving the detection requirements of greater depth and higher precision. This special issue presents eight articles covering the methods, techniques, software, and applications of SOTEM, providing strong support for the growing need for high-resolution subsurface detection.

It is difficult to explore the overlapping double-layer waterlogged goafs using the transient electromagnetic method. The reason is that upper waterlogged goafs will hinder the propagation of the electromagnetic field, thus prolonging the observation of the lower waterlogged goafs and reducing the signal-to-noise ratio. Besides, the burial depths and layer spacings of double-layer waterlogged goafs affect the signal-to-noise ratio and the observation time of transient electromagnetic signals. By building a double-layer waterlogged goaf model based on the Majiayan coal mine in Shanxi, this study analyzed the electromagnetic field propagation under layer spacings of 25 m, 50 m, 75 m, and 100 m,and calculated the observation time of waterlogged goafs with different layer spacings. Furthermore, it quantitatively characterized the differences between induced voltages in the double-layer waterlogged goafs with different layer spacings using root mean square errors. Additionally, this study proposed the identification criteria for explorable lower waterlogged goafs based on the record errors and noise levels during the observation. The results of physical simulation experiments are as follows: The differences between the induced voltages of double-layered waterlogged goafs with different layer spacings occur mainly in the late stage; the differences between induced voltages gradually decrease as the layer spacing and the burial depth of upper waterlogged goafs increases; the difference between induced voltages is close to the noise level when the layer spacing is greater than 75 m. The actual detection of the double layer waterlogged goaf with a spacing of 75 meters was conducted in Majiayan Coal Mine, and the results showed that the lower waterlogged goaf was not effectively identified.Therefore, It is difficult to effectively explore the lower waterlogged goafs when the layer spacing is greater than 75 m.

This study synthesized microtremor signals using the normal mode superposition.The dispersion curves of the synthesized microtremor signals were calculated using the spatial autocorrelation method,and the calculated results agreed well with theoretical dispersion curves.The simulation of microtremor signals involves many parameters,which are of great significance for microtremor exploration.As shown by results from numerical experiments of these parameters,the hypocentral distance and array size had a significant influence on the results.Moreover,high-order surface waves should be considered for complex strata,while small-size arrays tended to yield high-frequency dispersion information at quiet observation sites,thus improving the resolution of shallow strata.Therefore,it is necessary to consider the influences of hypocenter distribution,array size,and high-order surface waves on exploration results in microtremor exploration.

Since the periphery of the Xishan rare earth deposit in Weishan County, western Shandong is mostly covered by the Quaternary strata, single geophysical exploration methods are ineffective in searching for rare earth elements in this area. To establish a geological-geophysical prospecting model for deep rare earth prospecting in this area, a combination of exploration techniques and methods suitable for the deep exploration of rare earth deposits in this area were selected through multiple geophysical exploration technology experiments on the known geological profiles. The distribution range of the underground Mesozoic Xishan alkaline complex was roughly determined through gravity survey and high-precision magnetic survey. The ore body outcrop was delineated through ground-based gamma spectrometry, and the deep ore body characteristics were revealed through drilling. Finally, this study developed an integrated geophysical exploration method including gravity-magnetic joint delineation of rock masses, radioactive positioning for ore body outcrops, and deep drilling. By using this exploration model, one super-large rare earth deposit was discovered in this area, providing a reference for the exploration of rare earth deposits in the surrounding area.

The grounded-source transient electromagnetic (TEM) method, which enjoys the advantages of high topographic adaptability and large exploration depths, is suitable for deep resource exploration in mountainous areas. However, the TEM responses can be distorted due to topographic effects, causing great difficulties in data interpretation. This study investigated the influence patterns and correction method of topographic effects based on the three-dimensional unstructured time-domain finite element method. First, this study conducted the fine-scale description of mountains using unstructured tetrahedral grids, calculated the response of various topographic models, and analyzed the influence patterns of topographic effects. Then, it proposed a correction method for topographic effects based on the principle of the linear superposition principle of electromagnetic fields, established a geoelectric model of mountains according to the actual elevation data, and calculated the model responses through three-dimensional forward modeling. Subsequently, this study determined the topographic responses by subtracting the flat Earth model responses from the mountain model responses and then obtained the corrected TEM responses by removing the topographic responses from the total responses. The results are as follows: (1) The influence of mountains on the TEM responses is concentrated in the early stage and weakens gradually with time; (2) The topographic effects are concentrated near mountains, and their intensity depends on the distance of survey points from mountain peaks; (3) The influencing range and response amplitude of mountains are proportional to the mountain scale. In other words, a larger mountain scale corresponds to a larger influencing range and higher response amplitude; (4) Mountains with relatively high resistivity show more intense topographic influence. As shown by multiple models with simple and regular topographic anomalies, the corrected TEM responses, which match well with the responses from direct forward modeling, can effectively eliminate topographic effects to a certain extent. The research on the influence and correction method of topographic effects can be used as a reference for the processing and interpretation of TEM data of areas with complex terrain.

Southern Ningxia, located in a typical loess tableland area, hosts five semi-concealed - semi-exposed faults as boundaries of tectonic units. Based on the regional geotectonic conditions and outcrops, this study analyzed the distribution of the geophysical anomaly field in the study area, ascertained the distribution morphology of the concealed fault sections and the relationship between the faults, and established the fault framework in southern Ningxia. Based on the 1:200000 regional gravity and aeromagnetic data, this study extracted the weak signals of deep gravity and magnetic anomalies reflecting faults using both the multi-scale wavelet decomposition technique and the boundary recognition method and compared these signals with the deep faults depicted based on MT profiles. The results show that the five major faults in the study area are the boundaries of the significant gravity high anomaly zones in the detailed second-order wavelet field of gravity. The Niushoushan-Luoshan-Kongtongshan fault is the boundary between the north-south-trending long strip-shaped gravity anomalies and the north-west-trending flaky and banded gravity anomalies. This fault has typical dextral strike-slip characteristics and is the boundary fault between the Alxa microcontinent and the Ordos block. The Haiyuan fault is divided into Haiyuan faults Nos. 1 and 2 at depth. The No. 1 Haiyuan fault is concealed in the Haiyuan Basin and does not exhibit gravity anomalies. Moreover, the aeromagnetic anomaly field of this fault has significant zoning characteristics. The No. 2 Haiyuan fault is exposed at the northeastern feet of the northern and southern Mount Huashan and exhibits distinct characteristics of linear gravity anomalies but weak aeromagnetic anomalies. The two faults jointly constitute the composite boundary between the Early Paleozoic North Qilian Orogenic Belt and the Alxa microcontinent. Three faults in the Alxa microcontinent, namely the Tianjingshan fault, the Yantongshan-Yaoshan fault, and the fault at the eastern piedmont of Luoshan, are present as the northeastern boundary of the arcuate high-amplitude gravity anomaly zone.

To improve the detection level of municipal roads for rapid and effective municipal road collapse warning and rapid search for municipal pipe network distribution, the 22^nd Research Institute of China Electronics Technology Group Corporation designed and developed real-time three-dimensional ground-penetrating radar (3D GPR). With the real-time 3D GPR, which is based on the architecture of field programmable gate array and digital signal processor (FPGA&DSP), the institute achieved the design and implementation of several key technologies for the multi-channel high-speed acquisition system, enriching the road detection techniques and methods. The real-time 3D GPR enables high-speed acquisition of ten-channel radar data using the horizontally polarized antennae equipped with five transmitters and six receivers. The channels can be switched using high-speed switches, which operate in an interactive interpolation manner. The 3D GPR allows for up to 32 channels and detection speeds of above 60 km/h (channel interval: 2 cm). This is attributed to the switching of the antenna array using switches. The optimum antenna polarization design was verified by the comparison of experimental data from cavity- and metal-plate-based experimental sites. As a result, the optimal antenna scheme was determined. The measured results show that, compared to general LTD-2600 radar, the real-time 3D GPR boasts a higher acquisition speed and higher performance in terms of amplitude and phase, conducive to the improvement of road disaster detection technologies. Therefore, there is high market demand for the real-time 3D GPR.

Airborne geophysical surveys, characteristic of being green, economical, efficient, and subjected to less influence by surface factors, serve as the one of most effective means of basic surveys and scientific research on the Qinghai-Tibet Plateau. This study reviewed the progress in the airborne geophysical surveys in the Qiangtang Basin of the Qinghai-Tibet Plateau in the past thirty years, systematically summarizing the progress and geological interpretation results of comprehensive airborne geophysical surveys in the basin. Furthermore, this study presented research progress and understanding of major basic geological issues of the basin, such as the basin's boundaries, central uplift zone, basement properties, deep structures, and cover characteristics, as well as the identification of favorable structural areas for oil and gas exploration. Finally, based on an analysis of the developmental trends of airborne geophysical surveys in the Qiangtang Basin, this study proposed opinions and suggestions for key research directions in the future.

This study integrated the data of both the multi-purpose regional geochemical survey and land quality geochemical survey covering an area of 33 092 km² in eastern Qinghai. Based on these data, the total organic carbon storage of topsoil in the study area was estimated to be 171.16 Mt, with an average organic carbon density of 5 172.14 t/km². Moreover, this study analyzed the spatial distribution and main influencing factors of organic carbon in topsoil. As indicated by the results, the average density of organic carbon in topsoil is significantly high in high and middle-low mountains, grassland and meadow soils, soil parent materials of eluvial-slope deposits, forest grasslands, and alpine sparse vegetation areas, grassland and forest and is the lowest in deserts, aeolian sandy soil, and soil parent material areas of aeolian sands. This finding means that factors including topography (altitude), soil parent materials, climate, and vegetation affect the density and distribution of organic carbon in topsoil. Compared with the organic carbon storage revealed by the second general detailed soil survey in Qinghai, 53.21 Mt of organic carbon has been released from the topsoil of eastern Qinghai in the past 20 years. This result indicates that the soil organic carbon has decreased to a certain extent under the influence of human production activities such as long-term cultivation, overcutting, and overgrazing.

The Tonglvshan ore field is the most important skarn copper-iron-gold polymetallic ore field in the southeastern Hubei ore concentration area. Since its mineralization is closely related to Tonglvshan stocks, ascertaining the deep distribution and morphologies of these stocks and their contact relationship with surrounding limestones and marbles holds great significance for deep prospecting prediction of the ore field. This study first conducted a detailed analysis of the gravity and magnetic anomaly combinations of the Tonglvshan pluton and stocks; limestones and marbles, as well as their xenoliths; and skarn ore bodies and mineralized bodies. Accordingly, this study inferred the boundary of the Tonglvshan pluton and delineated the xenoliths and mineralized bodies of limestones and marbles within the Tonglvshan pluton. Then, this study conducted the 3D geological modeling based on the results from the 3D physical property inversion and 2.5D and 3D gravity-magnetic human-computer interaction inversion, as well as the drilling and geological data. Finally, this study established a 3D geological model for the plutons and mineralized bodies at depths of 4000 m and below in the Tonglvshan ore field, providing a basis for target delineation and deep prospecting prediction.

Huize County of Yunnan Province is situated in the karst area in southwestern China, where karst groundwater is its primary water source. To conquer local difficulties in drinking water, this study constructed a conceptual model of groundwater occurrence by fully investigating the hydrogeological conditions of the Huize area. Moreover, this study evaluated the applicability and optimal combination of geophysical methods based on the measurement results of petrophysical properties. According to the actual local needs, this study deployed a comprehensive profile combining high-density electrical resistivity tomography (HDERT) and audio magnetotellurics (AMT) in Tuogu Village, Huize County. The groundwater enrichment site was delineated relying on resistivity anomalies, effectively guiding the layout of boreholes. The boreholes achieved the maximum single-borehole water yield of 20.76 m³/d, thus effectively alleviating the local drinking water problem. The HDERT-AMT combined exploration method proves to be optimal for prospecting for groundwater in carbonate rock areas. HDERT can accurately characterize weathered layer thicknesses, bedrock boundaries, fissure evolutionary degrees, and water-bearing properties of strata, constraining groundwater recharge channels, thus counteracting AMT's defects for identification of near-surface stratigraphic structures. AMT can accurately reflect the spatial structures of fracture zones and the macrostructures of strata, limiting the boundary conditions (aquicludes) of water-bearing structures, thus making up for the defects of insufficient detection depths of HDERT in high-resistivity stratigraphic regions. HDERT and AMT, which are complementary to each other in terms of accuracy and depth, can be applied to identify and constrain the spatial occurrence conditions of groundwater migration, storage, and enrichment.

Since individual geophysical exploration methods suffer the multiplicity of solutions, comprehensive geophysical prospecting has been extensively applied in deep ore prospecting presently. This study conducted the geological exploration of the Duhu porphyry copper deposit in Xinxing County using multiple geophysical methods such as high-precision magnetic survey and controlled source audio-frequency magnetotellurics (CSAMT). It was inferred that the CSAMT-derived medium-low resistivity anomalies and the low-gentle anomalies derived from the high-precision magnetic survey serve as significant prospecting indicators. Satisfactory results were achieved in follow-up verification of the anomalies. Specifically, copper, molybdenum, silver, and gold mineralized bodies with a cumulative thickness of 178.2 m were identified in a 1 000 m deep borehole, with the highest copper grade of 1.45%. The application of comprehensive geophysical prospecting holds great significance in guiding the exploration of porphyry copper deposits in western Guangdong.

With the rapid development of cities and the accelerated construction of subway tunnels,there is an urgent demand for the detection of unfavorable geological bodies ahead of tunnel excavation.It is difficult for traditional electromagnetic methods to yield excellent detection results in an urban environment with high electromagnetic interference.Active-source surface wave exploration has gained increasing popularity in shallow superficial exploration and engineering geophysical prospecting in cities due to its strong anti-interference,convenient acquisition devices,and low construction cost.However,the traditional active-source reflection seismic method uses only a heavy hammer with limited excitation energy as a seismic source,and the collected signals are prone to be disturbed by urban activities.Meanwhile,the asphalt or cement pavement in urban areas is unfavorable for the placement of geophones and the excitation of seismic signals from a hammer.Given these,this study improved the geophones and seismic source devices at low costs,obtaining a more efficient and user-friendly surface wave acquisition device.As confirmed by practical engineering exploration,the improved device can collect surface-wave signals with strong energy and high signal-to-noise ratios,resulting in high-quality data,desirable inversion and imaging results,and high consistency between the geological defects and actual geological conditions.The improved acquisition device can be extensively promoted and referenced in active-source surface wave exploration in cities.

Magnetotelluric sounding (MT) has been extensively applied in mineral resource exploration. However, strong anthropogenic electromagnetic interference severely constrains the acquisition of high-quality original MT data. This study provided a detailed summary of the common types of electromagnetic noise sources in China and analyzed the characteristics of electromagnetic noise they produced. By comparing the methods for MT electromagnetic noise reduction at home and abroad, this study developed a rapid and effective construction and processing technology for MT data denoising in high-interference ore districts based on actual production demands. The results indicate that Robust processing, remote reference technique, and manual selection are effective and necessary in enhancing MT data quality. Besides, theoretical calculations suggest that the distance between the remote reference stations should be set at 3.56-fold skin depth or above, as verified by the MT experiments in the ore district of the Hongze salt basin, Jiangsu Province.

The performance of ray-based tomography inversion is affected by many factors,such as initial model error and low-velocity interlayer.The conventional tomography method based on first-arrival wave travel time,which constrains or smooths models,destroys the relative relationship between model parameters and rays and affects the inversion stability.By testing the performance of first-arrival wave travel time-based tomography inversion under different initial models,this study proposed a first-arrival wave travel time-based tomography inversion method with surface wave information as constraints.The process of this method is as follows:(1)Given that surface waves feature high energy and frequency dispersion in seismic data,the surface-wave frequency dispersion curves are obtained through the multi-channel analysis of surface waves;(2)Using the damped least squares method,the shallow-surface shear wave (S-wave) velocities are determined through inversion;(3)With the S-wave velocity structure as the constraint,the initial compressional wave (P-wave) model is established,and accordingly,the first-arrival wave travel time-based tomography inversion that considers regularization is achieved.This method improves the accuracy and stability of shallow structure inversion by fully utilizing the surface wave information in seismic data to counteract the inherent defects of tomography inversion.The effectiveness of this method has been verified using actual data.

Significant aeromagnetic and gravity anomalies were found in the ultra-deep coverage zone of the Pandian area in the northwestern Shandong Province. Through systematic verification of gravity and magnetic anomalies, a breakthrough in prospecting for deep skarn iron deposits has been achieved through several boreholes around the Pandian gravity-magnetic anomaly zone. However, the gravity-magnetic anomaly zone spreads extensively and its characteristics cannot directly indicate the prospecting target, thus some boreholes failed to find ores or revealed poor ore-finding conditions. Hence, to accurately delineate the ore-forming location in the gravity-magnetic anomaly zone and achieve a further breakthrough in ore prospecting, this study conducted the wide-field electromagnetic (WFEM) sounding in the verified Pandian gravity-magnetic anomaly zone. Combining the drilling verification, this study delineated the deep ore-forming interval of skarn iron deposits in the deep coverage zone and the favorable structural plane for ore-forming, suggesting the deep fine-scale prospecting targets.

Low-density geochemical mapping is characterized by high order streams to be sampled and a large coverage area and can be used to effectively trace geochemical blocks with high metal contents. Based on the 1:1,000,000 low-density geochemical mapping data of Ethiopia and the processing of the testing data of Cu in the original stream sediments, this study calculated the anomaly threshold of Cu at 37×10^-6 through iterative deletion. Then, this study delineated three geochemical blocks and two regional anomalies with 37×10^-6, 42×10^-6, 47×10^-6, 52×10^-6, 59×10^-6, and 66×10^-6 as grading intervals. It calculated the mineralization coefficient of Cu ore bodies in the study area at 0.055% by referencing the known reserves of Cu deposits in geochemical blocks with a high level of copper exploration in the same metallogenic belt. Moreover, this study estimated the Cu resources in the study area at 2,600,000 t based on a rock mass thickness of 1,000 m. By combining the analysis of metallogenic geological conditions, this study determined that the zones where geochemical blocks nos. 2, 3, and 4 are located can be considered key metallogenic prospect areas for further detailed exploration.

To explore the critical factors influencing the results of microtremor-based exploration at a depth of thousands of meters,this study conducted experiments using triangular arrays based on spatial autocorrelation(SPAC) and extended SPAC(ESPAC).Focusing on factors such as array size,acquisition unit frequency,and acquisition duration,this study explored the frequency band ranges corresponding to different array sizes,the arrangement of arrays in kilometer-depth exploration for obtaining both deep and shallow data,and the improvement in deep resolution.Based on the analysis and discussion results,this study established a parameter-setting system to improve the accuracy of exploration at a depth of thousands of meters.

Owing to the poor physical properties,the tight reservoirs in the Jimusaer Sag can yield industrial oil flow only through hydraulic fracturing.The research on mechanical properties and the brittleness assessment of rocks can provide a certain reference for hydraulic fracturing.This study obtained the mechanical properties of the tight strata in the Jimusaer sag using triaxial mechanical tests and determined the log parameters potentially sensitive to rock brittleness by analyzing the correlation between the sensitivity of the brittleness index and logs.Then,based on the grey correlation theory,this study determined the initial sequence of sensitivity parameters and normalized the parameters selected.Then,it quantitatively correlated the selected parameters with the potential sensitivity to the brittleness index and determined the degrees of correlation and their order.On this basis,this study established a matrix for the pair-wise comparison of the sensitivity parameters using the analytic hierarchy process (AHP) and determined the weight vector.Then,it established the functional relationship model between the brittleness index and the sensitivity parameters,thus developing a new prediction model for the brittleness index.Finally,this study compared the log models with the brittleness model established based on mechanical properties and the brittleness index determined through laboratory tests.The study results are as follows.The tight strata in the Jimusaer Sag have high brittleness,and the comprehensive brittleness index characterized using the whole-process stress-strain curve agreed with the actual brittleness characteristics of rocks.The degree of correlation of the sensitivity parameters determined using the grey correlation method was in the order of natural gamma-ray(GR)>resistivity(R_t)>density(ρ)>neutron(CNL)>sonic interval transit time(ΔT),which had a weight coefficient of 0.33,0.22,0.18,0.16, and 0.11,respectively in the new prediction model.The prediction method proposed in this study was applied to the Lucaogou Formation in the Jimusaer Sag.Compared with that determined through laboratory tests,the brittleness index predicted can reflect the actual brittleness of the formation,exhibiting a high consistency.As shown by the results from well tests,the productivity index of oil was proportional to the brittleness index,and a higher brittleness index was associated a high production capacity after fracturing.Therefore,the new method provides a new approach to brittleness index prediction and guides the parameter selection for the fracturing of reservoirs.

Ground-penetrating radar (GPR) data are often contaminated by random noise in the actual engineering inspection.The noise in data will reduce the signal-to-noise ratio and resolution of the data,adversely affecting the subsequent inversion and interpretation.Accordingly,this study proposed neural network-based denoising for GPR data.First,a multi-layer neural network model was constructed to integrate the data corrupted by white Gaussian noise into the noise-free data.Then,the corrupted data and their corresponding noise patches were built as training data.The weights of neurons in every layer of the model e updated using a back-propagation algorithm to minimize the model training loss.Finally,the two synthetic data and the measured radar data were input to the trained model,and the model's output was calculated using the noise characteristic weights acquired from the training.Compared with the curvelet transform,the numerical simulation test results verify the effectiveness and robustness of the method proposed in this study.Moreover,the proposed method can suppress the noise more thoroughly in areas with complex structures and weak amplitudes,and show effective signals more clearly.

The Niuxingba plumbum-zinc-gold-silver deposit (the Niuxingba deposit) occurs in the Yinkeng ore field at the intersection of the EW-trending Nanling metallogenic belt and the NNE-striking Wuyishan metallogenic belt. It is a typical hydrothermal vein deposit under the strict control of fault structures, with ore bodies occurring as vein groups. To predict the deep prospecting potential of the No. V31 major ore belt (body) of the Niuxingba deposit, this study systematically investigated the axial (vertical), transverse, and longitudinal geochemical characteristics and zoning of tectonic primary halos of the ore belt (body) based on the geological characteristics of the deposit. Then, this study determined the axial zoning sequence and the geological-geochemical model of tectonic primary halos. It was confirmed that this model was correct, reasonable, and reliable using the multivariate statistical method. The results of the geological-geochemical model show that: ① the front halo of the Niuxingba deposit has F as the indicator element; ② the near-ore halo has two types of indicator elements: the gold mineralization-related As-Au element association in the middle and upper parts of the ore body and the Pb-Zn-Ag mineralization-related Hg-Zn-Pb-Ag-Cu-Bi-Sb element association in the middle part of the ore body; ③ the rear halo has the Mo-Cr-Co-Ni element association as indicator elements; ④ the anomaly centers of the front, near-ore, and rear halos are about 200~300 m apart axially, suggesting significant coexistence of front and rear halos and the presence of inflection points of the near-ore halo broken line. Furthermore, the transformation of low-moderate-temperature Pb-Zn-Ag-Au mineralization into moderate-high-temperature Cu-Zn mineralization occurs eastward. These characteristics indicate that the No. V31 main ore belt (body) has a pitch direction of east and a large extension toward the deep part (to an elevation of -200 m at least), implying that blind ore bodies may occur. As verified by deep drilling in the eastern concealed area (the lowest ore-controlled elevation of the No. 367 survey line: -165 m), the eastern deep part of the No. V31 ore belt (body) has a high potential for increasing reserves.

Time-frequency analysis (TFA) has been widely used in seismic exploration,thus it is crucial to develop a TFA algorithm with high time-frequency resolution.Given the limitations of conventional TFA methods,this study proposed a TFA method based on the regularization theory.The proposed method considers the signal in a short-time window as a superposition of harmonics with different frequencies and takes the TFA problem as an inverse problem.From this perspective,the TFA problem is ill-posed and needs to be solved based on the regularization theory to get a significant time-frequency spectrum.The solution methods under the conditions of L₁ and L₂ norm constraints and the minimum support constraint are commonly used in the regularization theory.This study investigated these solution methods and unified them into the same solution framework.Numerical analysis shows that the TFA method under the condition of the minimum support constraint yielded high time-frequency resolution.This method was systematically applied to the actual data of a specific study area,producing a time-frequency data volume with high time-frequency resolution.Moreover,the planar reservoir distribution was clearly characterized using a single-frequency data volume,demonstrating the promising application prospect of the method.

Xiong’an New Area is one of the areas with the best conditions for the development and utilization of geothermal resources in sedimentary basins of eastern China. Wumishan Formation of Jixian System is the main thermal reservoir, with buried depth of the top boundary varies greatly, which istypical carbonate type thermal reservoir. In order to find out the stratigraphic structure and concealed faults within 6 km of the starting area of Xiong’an New Area, focus on finding out the spatial distribution and structural characteristics of the main deep thermal reservoirs, and predict the favorable geothermal areas, the time-frequency electromagnetic method is applied to the geothermal resources exploration of Xiong’an New Area. Through high-standard data acquisition, refined data processing and resistivity-constrained inversion, the pseudo-seismic imaging technology and borehole data are used to calibrate the resistivity horizon, which effectively improves the reliability of interpretation results. In this work, 8concealed faults were identified, mainly NNE strike normal faults, which controlled the salient-depression pattern and stratigraphic distribution of the study area. The study area is divided into Rongcheng salient, middle sub-depression, Niutuozhen salient and Baxian depression from west to east. The thermal reservoirs of Wumishan Formation is mainly distributed in Niutuozhen salient, Rongcheng salient and middle sub-depression, with buried depth of top interface is about 600~2600m. Vsing the inversion results of the time-frequency electromagnetic method, the three-dimensional geological model of the study area is constructed, and the Niutuozhen salient area is considered to be the optimal geothermal favorable area from the aspects of heat source, channel, reservoir, caprock and fluid, especially near the footwall of F₄.

Audio magnetotellurics (AMT) is widely used for energy and mineral explorations because of its high exploration efficiency and high vertical resolution. Using a three-dimensional (3D) inversion algorithm based on data space, this study performed 3D inversion of the AMT data collected from geothermal exploration in the Santunhe area of Xinjiang. As indicated by the inversion results, the 3D inversion avoids the influence of inhomogeneous geobodies on the survey lines in the study area and yielded very rich and intuitive 3D geoelectric anomalies. In combination with the geological data and the 3D inversion results, this study analyzed the subsurface electrical properties of the study area and the formation water-bearing properties related to geothermal reservoirs, and finally inferred several favorable areas for geothermal reservoirs from the geothermal accumulation patterns of the study area.

Located in the loess tableland area,the eastern Ordos Basin features criss-cross ravines and gullies and great topographic fluctuations.Its complex surface conditions and near-surface structures caused significantly different amplitudes,frequencies,and phases in the original seismic data of different regions.These differences are unrelated to the subsurface geological information and can easily lead to misinterpretation.Therefore,there is an urgent need to develop a processing method for seismic data consistency according to the characteristics of seismic data in the study area,aiming to improve the fidelity of seismic data.Based on the summary of the current consistency processing methods,this study built a new consistency processing flow for seismic data under complex surface conditions.By innovating surface consistent amplitude compensation,this study employed the dual-domain near-surface Q-absorption compensation for the first time to broaden the frequency band and improve the amplitude and frequency consistency of seismic data collected across gullies and tablelands.In addition,this study applied the surface consistent deconvolution of Yu's wavelet to attenuate the low-frequency noise and broaden the effective signal frequency band,improving the signal-to-noise ratio,resolution,and wavelet consistency of seismic data.The actual application verifies that the method used in this study is feasible and effective and has a high popularization value.

Previous studies of associated elements of the No. 510 uranium deposit in Sichuan mostly focus on individual ore blocks. To classify the types of associated resources in the whole deposit, this study conducted a comprehensive comparative analysis based on the investigation of horizontal and vertical zoning of associated elements of uranium ores, as well as the existing study results of rock and deposit geochemistry and metallogenic regularity. Accordingly, this study ascertained the zoning characteristics of associated minerals in the whole deposit. In the vertical direction, the deposit was divided into three mineral assemblage zones: the iron-nickel sulfide-uranium mineralization zone, the low-content sulfide-uranium mineralization zone, and the sphalerite-low-content iron-nickel sulfide-uranium mineralization zone. In the horizontal direction, the deposit was divided into the upper Ni, V → Zn → Ni (low-content Cu) and the lower Mo, Ni, Zn, V → Zn, Ni → Mo, Ni, Zn → Zn (low-content Cu) metallogenic element assemblage transition zones. The smelting and recovery experiments were completed for uranium and associated metals such as molybdenum, nickel, and zinc in the deposit, increasing the economic value of the deposit and expanding economic benefits. This study determined six types of associated resources for the No. 510 uranium deposit and comprehensively evaluated the utilization of associated elements, providing theoretical guidance for both the deep prospecting prediction and the prospecting of replacement resources in similar mines.

As an inevitable physical phenomenon in the application of frequency-domain electromagnetics, the static shift effect is generally suppressed or eliminated by correction. This study proposed a new approach of directly utilizing the static shift effect of natural electromagnetic methods to explore shallow electrical anomalies. The frequency selection method of telluric electricity field (FSM) is to study the variations in electrical properties of subsurface media by measuring several horizontal electric field components with different frequencies generated on the surface by the natural alternating electromagnetic field. In this study, the forward modeling of FSM data was conducted using the two-dimensional finite element method. The modeling results are shown as follows: (1) In the case of low-resistivity anomalies near the surface, the curves of horizontal electric field components along the survey line on the surface showed the same morphologies as the FSM-derived curves, with significant low-potential anomalies above the low-resistivity anomalies; (2) As the calculated frequencies increased, both the profile curves and the pseudosection map of electric field components exhibited a static shift effect, indicating that the FSM-derived anomalies were mainly caused by the static shift effect. Both the FSM application results and the drilling verification results showed that with the presence of groundwater, the FSM-derived profile curves and pseudosection map exhibited a significant static shift effect, which was consistent with the CSAMT exploration results. As indicated by theoretical and practical research, it is feasible to directly use the components of the telluric electricity field for the exploration of shallow electrical anomalies. Moreover, shallow geological exploration can be conducted by utilizing the static shift effect of the frequency domain electromagnetics.

This study aims to ascertain the heavy metal pollution of groundwater in a typical chemical industry park in northwestern Shandong. According to the investigation and evaluation requirements for groundwater environments in chemical industry parks, this study collected 10 groundwater samples to analyze the concentrations and spatial distributions of eight heavy metals, namely Fe, Cu, Zn, Al, Cd and Pb. Furthermore, it conducted the health risk assessment of groundwater for different populations. The results indicate that: (1) except Mn and Al, all heavy metals in the groundwater of the chemical industry park showed concentrations lower than the class III water quality standard stated in the Standard for Groundwater Quality (GB/T 14848—2017), with a comprehensive pollution index ranging from 0.37 to 0.78. The monitoring points for heavy metal elements are all pollution-free; (2) the overall spatial distributions of heavy metals are roughly consistent with the distribution areas of key enterprises in the chemical industry park. This consistency indicates that external factors such as the production activities of enterprises affect the spatial distributions of heavy metals in groundwater; (3) the health risks are lower for children than for adults and lower via skin contact than via drinking. The non-carcinogenic risks under different exposure routes are acceptable for different populations. Carcinogens As and Cd have slight carcinogenic risks for adults. Local authorities should strengthen the supervision of the production activities of enterprises and thoroughly inspect enterprises with suspected pollution. Only in this way can we effectively control and then gradually reduce the risks to human health caused by groundwater pollution.