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Distribution of microorganisms in the typical geothermal field environment and its significance for geothermal exploration
ZHENG Xu-Ying, XU Ke-Wei, GU Lei, WANG Guo-Jian, LI Guang-Zhi, GUO Jia-Qi, ZOU Yu, BORJIGIN Tenger
Geophysical and Geochemical Exploration    2023, 47 (5): 1127-1136.   DOI: 10.11720/wtyht.2023.1151
Abstract323)   HTML18)    PDF (4903KB)(308)      

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.

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Advancements in research on geochemical exploration methods and technologies for mineral resources in overburden areas
SUN Yue, ZHANG Zhen-Yu, FENG Bin, YANG Shao-Ping, WANG Zhi-Feng
Geophysical and Geochemical Exploration    2023, 47 (6): 1387-1399.   DOI: 10.11720/wtyht.2023.0109
Abstract266)   HTML15)    PDF (2899KB)(366)      

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.

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Gravity survey and audio magnetotellurics-based insights into the deep structures and geothermal resource potential of the Rucheng Basin
ZHAO Bao-Feng, WANG Qi-Nian, GUO Xin, GUAN Da-Wei, CHEN Tong-Gang, FANG Wen
Geophysical and Geochemical Exploration    2023, 47 (5): 1147-1156.   DOI: 10.11720/wtyht.2023.1449
Abstract242)   HTML8)    PDF (8018KB)(361)      

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.

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Aerogeophysical anomalies and prospecting direction in the Fengtai ore concentration area
XU Xue-Yi, XIONG Sheng-Qing, YANG Xue, GAO Wei-Hong, FAN Zheng-Guo, JIA Zhi-Ye
Geophysical and Geochemical Exploration    2023, 47 (5): 1157-1168.   DOI: 10.11720/wtyht.2023.0068
Abstract232)   HTML10)    PDF (14675KB)(325)      

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.

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Application of the opposing-coils transient electromagnetic method in urban geological surveys
HE Sheng, WANG Wan-Ping, DONG Gao-Feng, NAN Xiu-Jia, WEI Feng-Feng, BAI Yong-Yong
Geophysical and Geochemical Exploration    2023, 47 (5): 1379-1386.   DOI: 10.11720/wtyht.2023.1554
Abstract223)   HTML4)    PDF (5856KB)(349)      

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.

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An experimental investigation of the CO2 and SO2 gas geochemical survey method for mineral exploration in forested areas
WAN Wei, WANG Ming-Qi, CHENG Zhi-Zhong, FAN Hui-Hu, ZUO Li-Bo, LI Jun-Hui
Geophysical and Geochemical Exploration    2023, 47 (5): 1137-1146.   DOI: 10.11720/wtyht.2023.1615
Abstract219)   HTML9)    PDF (4627KB)(192)      

This study aims to explore the feasibility of the carbon dioxide (CO2) and sulfur dioxide (SO2) gas geochemical survey method for mineral exploration in forested areas. Based on the newly designed gas rapid analysis instrument, this study conducted an experimental investigation of the method in the forested Jiapigou gold concentration area, Jilin Province. The results show that significant CO2 and SO2 anomalies were observed above the concealed ore bodies and structures. In the forested area, the CO2 and SO2 gas geochemical survey method reflected the fault structures and effectively indicated the deep concealed gold deposit. This method holds critical significance for the breakthrough of prospecting technology in China's covered areas.

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First-arrival wave travel time-based tomography inversion with surface wave information as constraints
ZHANG Li-Zhen, SUN Cheng-Yu, WANG Zhi-Nong, LI Shi-Zhong, JIAO Jun-Feng, YAN Ting-Rong
Geophysical and Geochemical Exploration    2023, 47 (5): 1198-1205.   DOI: 10.11720/wtyht.2023.1536
Abstract214)   HTML2)    PDF (4925KB)(256)      

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.

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Application of integrated geophysical exploration technology in the geothermal exploration of northern Jinan
ZHANG Yi, LIU Peng-Lei, WANG Yu-Min, ZHANG Peng-Peng, ZHANG Chao, ZHANG Ning
Geophysical and Geochemical Exploration    2024, 48 (1): 58-66.   DOI: 10.11720/wtyht.2024.1141
Abstract213)   HTML9)    PDF (8896KB)(382)      

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.

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Prospecting for concealed skarn iron deposits using the high-precision gravity-magnetic survey method
DONG Jian, LI Xiao-Peng, FU Chao, DANG Zhi-Cai, ZHAO Xiao-Bo, ZENG Qing-Bin, HU Xue-Ping, WANG Jin-Hui
Geophysical and Geochemical Exploration    2024, 48 (1): 31-39.   DOI: 10.11720/wtyht.2024.1047
Abstract207)   HTML7)    PDF (7885KB)(325)      

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.

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Comparison and summary of different azimuthal anisotropy-based inversion techniques
LIANG Zhi-Qiang, LI Hong
Geophysical and Geochemical Exploration    2024, 48 (2): 443-450.   DOI: 10.11720/wtyht.2024.1251
Abstract206)   HTML3)    PDF (3440KB)(145)      

The progress in seismic acquisition techniques characterized by wide azimuths,wide frequency bands,and high densities has greatly promoted the application of the prestack P-wave fracture inversion technique based on the azimuthal anisotropy theory.Azimuthal anisotropy-based inversion can yield the azimuths and intensities of fractures.However,different inversion techniques yield different parameters for fracture intensity characterization,resulting in inconsistent inversion results.Consequently,the azimuthal anisotropy-based inversion results of fractures are non-unique,leading to confusion about accurate results.Based on the Thomsen anisotropy theory,as well as the interrelationships between fracture models(the Hudson coin model and the Schoenberg linear sliding model),this study established the connections of anisotropic parameters between different fracture inversion techniques(VVAZ,Ruger's approximation,and Fourier series),presenting the real meanings and mathematical expressions of results from different azimuthal anisotropy-based fracture inversion techniques.Additionally,this study summarized the relationships of parameters between different inversion techniques and fracture models,further deepening the research on azimuthal anisotropy-based fracture inversion.This study lays solid theoretical and technical foundations for large-scale fracture detection based on the seismic data obtained using the seismic acquisition techniques featuring wide azimuths,wide frequency bands, and high densities.

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Regional geochemical characteristics and metallogenic prospect area prediction of strategic mineral antimony in the Eerguna block, Heilongjiang Province, China
WAN Tai-Ping, ZHANG Li, LIU Han-Liang
Geophysical and Geochemical Exploration    2023, 47 (5): 1179-1188.   DOI: 10.11720/wtyht.2023.1439
Abstract202)   HTML4)    PDF (4012KB)(193)      

The Eerguna block with metallogenic geological conditions is an important metallogenic area in Heilongjiang Province. Globally, China boasts the richest resource of antimony. However, the high mining intensity in recent years imposes huge challenges to this resource advantage of China. In this context, it is necessary to ascertain the geochemical characteristics of antimony in the Eerguna block. Based on the data of the 1∶250 000 stream sediment survey in the Eerguna block, this study explored the geochemical parameters of antimony in different tectonic units and the regional geochemical anomalies of this block. The results show that the study area has median and average concentrations of antimony of 0.33×10-6 and 0.55×10-6, respectively. The Mohe foreland basin is rich in antimony, with median and average concentrations of antimony higher than those of the study area. Furthermore, zones with high and extremely high antimony concentrations in the study area are distributed primarily in the Mohe foreland basin. Based on the 85% cumulative percentage, this study determined 66 geochemical anomalies of antimony, among which two reach the scale of geochemical provinces. Furthermore, this study identified significant geochemical anomalies of antimony in the discovered gold, antimony, and plumbum deposits or ore occurrences (mineralization points). Based on the spatial distributions of geochemical anomalies and metallogenic geological conditions of antimony, arsenic, and gold, this study delineated three metallogenic prospect areas of antimony: the Beijicun-Sanlianshan metallogenic prospect area, the Wangsushan-Daling metallogenic prospect area, and the Baikalushan-Huzhong metallogenic prospect area. In addition, the geochemical anomalies and metallogenic prospect areas for antimony, arsenic, and gold provide important areas for searching for sulfide deposits such as gold, antimony, and plumbum ones in the study area.

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A review of thirty years of airborne geophysical surveys in the Qiangtang Basin and future prospect
ZHOU Dao-Qing, XIONG Sheng-Qing, WANG Bao-Di, CAO Bao-Bao, GUO Zhi-Hong, HU Yue, ZHENG Yu-Zhou, ZHAO Rui, WEI Yan-Yan, XIAO Meng-Chu, HU Xia-Wei, YAN Qiao-Juan
Geophysical and Geochemical Exploration    2024, 48 (2): 287-295.   DOI: 10.11720/wtyht.2024.1413
Abstract199)   HTML14)    PDF (7354KB)(237)      

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.

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Predicting the geothermal resources of the Tangyu geothermal field in Meixian County, Shaanxi Province, based on soil radon measurement and the controlled source audio magnetotelluric method
XUE Dong-Xu, LIU Cheng, GUO Fa, WANG Jun, XU Duo-Xun, YANG Sheng-Fei, ZHANG Pei
Geophysical and Geochemical Exploration    2023, 47 (5): 1169-1178.   DOI: 10.11720/wtyht.2023.0010
Abstract195)   HTML10)    PDF (4345KB)(337)      

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.

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Chronology and geochemical characteristics of trachytes in the Tiaojishan Formation, Xuanhua Basin, northwestern Hebei Province, and their geological implications
YANG Ji-Yuan, HU Xin-Zhuo, ZHOU Jing, QI Peng-Chao, LI Ze-Yang, MENG Jia-Bao, XU Fan, ZHANG Hui-Bin, QI Hui-Yun
Geophysical and Geochemical Exploration    2024, 48 (1): 1-14.   DOI: 10.11720/wtyht.2024.2503
Abstract188)   HTML14)    PDF (8237KB)(196)      

The Tiaojishan Formation in northwestern Hebei Province is home to volcanic-sedimentary strata. Due to the lack of fossil organisms, insufficient isotopic dating data, and outdated dating methods, the formation epochs of these strata have been controversial. To accurately determine their formation epochs and examine their regional geotectonic setting, this study conducted a detailed field investigation of the lithologic assemblage of the Tiaojishan Formation in the Xuanhua Basin. Petrological, petrogeochemical, and high-precision isotopic dating studies were conducted on the trachytic volcanic rocks in the upper segment of the formation, obtaining the LA-ICP-MS-based zircon U-Pb isotopic ages, which were 161.1±1.2 Ma and 162.5±1.3Ma. As indicated by the petrological and petrogeochemical characteristics, these trachytic volcanic rocks belong to the shoshonite series, exhibiting enriched light rare earth elements, relatively enriched elements including Rb, K, Th, Ce, Zr, and Hf, and relatively depleted Ba, Nb, Sr, P, and Ti. According to the comparison of principal parameters and graphical discrimination, the magma originated primarily from the melting of continental crustal materials and formed in the tectonic setting of compressional continental margin volcanic arcs. The comprehensive research reveals that the Tiaojishan Formation formed primarily during the Middle Jurassic and continued to the Late Jurassic, and the trachytic volcanic rocks in its upper segment formed in the intraplate compressional tectonic setting. The results of this study provide new data for the division and correlation of Mesozoic volcanic-sedimentary strata and the analysis of their formation environment.

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Advances in research on the distributed optical fiber acoustic sensing system in the field of geophysical exploration
ZHOU Shao-Yu, BAO Qian-Zong, SHI Wei
Geophysical and Geochemical Exploration    2024, 48 (2): 411-427.   DOI: 10.11720/wtyht.2024.1304
Abstract186)   HTML5)    PDF (7793KB)(216)      

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.

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Artificial neural network-based transient electromagnetic imaging
YOU Xi-Ran, ZHANG Ji-Feng, SHI Yu
Geophysical and Geochemical Exploration    2023, 47 (5): 1206-1214.   DOI: 10.11720/wtyht.2023.1547
Abstract185)   HTML3)    PDF (4517KB)(242)      

The transient electromagnetic method (TEM) commonly uses the all-time apparent resistivity parameter for interpretation, which involves complex formulas and time-consuming iterative processes. Based on the characteristics of TEM data, this study employed the artificial neural network (ANN) for TEM pseudo-resistivity imaging. First, this study designed a multi-hidden-layer BP neural network and calculated a response amplitude through TEM analysis. The response amplitude, as the mapping parameter of pseudo resistivity, was used for network training. Then new data outside the training set were used to test the trained network. A homogeneous half-space and one-dimensional layered model was built to verify the correctness and adaptability of the neural network. The imaging of the three-dimensional geoelectric model was performed. As revealed by the results, the pseudo resistivity calculated based on the neural network can reflect the target anomalies of the geoelectric model, with highly accurate network imaging results. Finally, the measured data were processed using the neural network algorithm, further indicating that the neural network-based imaging can serve as a basis for data interpretation. This study verified the feasibility of the ANN in TEM imaging, thus providing a new approach for TEM imaging.

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Calculation and analysis of zero drift rates of gravimeters in two-way reciprocal observations based on different specifications
CHANG Xiao-Peng, CHEN Liang, ZHANG Xiang, ZHANG Ling-Xiao, ZHU Zhang-Liu, QIAO Yan-Yi
Geophysical and Geochemical Exploration    2023, 47 (5): 1307-1315.   DOI: 10.11720/wtyht.2023.1526
Abstract185)   HTML0)    PDF (928KB)(184)      

Gravity survey is an important part of geodetic mapping and geophysical exploration. Different gravity specifications adopt different methods to calculate the zero drift rates in two-way reciprocal observations (i,j,j',i'). The repeated measurements of point j are subjected to static drift in the geological survey specification. By contrast, the zero drift rate is calculated through regression analysis in the petroleum specification. Different processing methods for the repeated measurement interval of point j yield significantly different zero drift rates based on the two specifications. Through theoretical formula analysis and comparison of measured data, this study analyzed the influence of g'j- g j and t'j-tj in the repeated measurements of point j on the calculation of the zero drift rate. By comparing with the regression analysis, this study illustrated the importance of static drift in reducing the uncertainties caused by instrument performance and measurement environment. Moreover, this study proposed the applicable conditions of the two specifications.

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A method for strong noise suppression based on DC-UNet
ZHOU Hui, SUN Cheng-Yu, LIU Ying-Chang, CAI Rui-Qian
Geophysical and Geochemical Exploration    2023, 47 (5): 1288-1297.   DOI: 10.11720/wtyht.2023.1386
Abstract175)   HTML0)    PDF (6456KB)(175)      

Seismic data acquired from mature industrial areas frequently contain a large amount of local strong noise with high amplitude due to the continuous operation of production equipment.However,such local strong noise can be hardly suppressed using conventional denoising methods.This study integrated dilated convolution(DC) and U-Net into a DC-UNet network for suppressing local strong noise.For the circular DC blocks at the front end of the DC-Unet network,a circularly expanded DC kernel was used to extract the features of strong noise at different scales,with the receptive field being expanded.Meanwhile,an encoder was used at the back end of the network to extract the features of strong noise and restore the details of strong noise.Subsequently,the DC-UNet network was employed to perform a nonlinear mapping from noisy data to noise.On this basis,strong noise was suppressed by subtracting the learned strong noise from the noisy data.As indicated by the experimental results of synthetic and real data obtained from the training using the PyTorch framework in the GPU environment,the DC-UNet network can effectively suppress the local strong noise and improve the signal-to-noise ratio compared with DnCNN,U-Net,and PCA-UNet networks.

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Application of comprehensive geophysical prospecting in exploration of the Duhu copper deposit in Xinxing County
HE Jun-Fei
Geophysical and Geochemical Exploration    2024, 48 (2): 375-381.   DOI: 10.11720/wtyht.2024.1101
Abstract175)   HTML11)    PDF (5778KB)(214)      

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.

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Feasibility of the transient electromagnetic method in the exploration of double-layer waterlogged goafs with different layer spacings in coal mines
ZHANG Fan, FENG Guo-Rui, QI Ting-Ye, YU Chuan-Tao, ZHANG Xin-Jun, WANG Chao-Yu, DU Sun-Wen, ZHAO De-Kang
Geophysical and Geochemical Exploration    2023, 47 (5): 1215-1225.   DOI: 10.11720/wtyht.2023.1525
Abstract163)   HTML6)    PDF (5416KB)(290)      

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.

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Design and implementation of key technologies for real-time three-dimensional ground-penetrating radar
YIN Da, XIN Guo-Liang, SUN Xue-Chao, ZHANG You-Yuan, ZHANG Qi-Dao
Geophysical and Geochemical Exploration    2024, 48 (1): 194-200.   DOI: 10.11720/wtyht.2024.1030
Abstract156)   HTML0)    PDF (3013KB)(217)      

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 22nd 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.

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Critical factors in microtremor-based exploration at a depth of thousands of meters
QI Juan-Juan
Geophysical and Geochemical Exploration    2024, 48 (3): 777-785.   DOI: 10.11720/wtyht.2024.1358
Abstract156)   HTML3)    PDF (6323KB)(157)      

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.

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Research and application of the log-based comprehensive identification method for low-contrast oil layers:A case study of the Lufeng oilfield in the Pearl River Mouth Basin
LIU Wei-Nan, GUAN Yao, LIU Dao-Li, SHI Lei, SONG Wei
Geophysical and Geochemical Exploration    2024, 48 (3): 573-583.   DOI: 10.11720/wtyht.2024.1164
Abstract154)   HTML14)    PDF (7267KB)(110)      

The accurate identification of fluid properties is critical for reservoir evaluation.However,for the Paleogene low-porosity and low-permeability reservoirs in the Lufeng area,Pearl River Mouth Basin,the low contrast between oil and water layers in conventional logs due to the presence of high-resistivity water layers complicates the identification of oil and water layers.This study first ascertained the reservoir characteristics and genetic analysis of low-contrast oil layers.Then,it developed the Flair gas logging response equation and the Flair logging response correction method,aiming to overcome the challenge that gas logging response values of low-porosity and low-permeability reservoirs are significantly influenced by factors such as drilling rate and porosity.Given the differences in the properties and components of various fluids,this study constructed new oil-bearing and water-content indices using Flair gas logging curves.Moreover,this study characterized the geochemical chromatogram using a gamma probability distribution function and extracted the shape and scale factors to describe the chromatogram characteristics.Based on sensitivity parameters,this study plotted the characteristic parameter-based fluid property identification chart.The practical application shows that the log-based comprehensive fluid property identification method can yield satisfactory effects,achieving a compliance rate of 91.3%.Therefore,this method can be popularized.

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Application of high-density electrical resistivity tomography and audio magnetotellurics for groundwater exploration in the karst area in southwestern China
XIA Shi-Bin, LIAO Guo-Zhong, DENG Guo-Shi, YANG Jian, LI Fu
Geophysical and Geochemical Exploration    2024, 48 (3): 651-659.   DOI: 10.11720/wtyht.2024.1237
Abstract150)   HTML5)    PDF (5894KB)(180)      

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.

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Exploring the Rayleigh wave propagation characteristics in different aggregate concrete models
XIANG Zhu-Bao, ZHANG Da-Zhou, ZHU De-Bing, LI Ming-Zhi, XIONG Zhang-Qiang
Geophysical and Geochemical Exploration    2023, 47 (5): 1226-1235.   DOI: 10.11720/wtyht.2023.0086
Abstract147)   HTML0)    PDF (1444KB)(181)      

To avoid aggregate interference on the detection target in concrete quality detection by Rayleigh waves, the abnormal signals from the aggregate and the target should be distinguished for high detection reliability. Hence, this study explored the propagation characteristics of Rayleigh waves in aggregate concrete. By building the mesostructural random aggregate models and employing the high-order staggered-grid finite difference scheme, this study examined the effects of the randomness, shape, size, and content of aggregate on the Rayleigh wave field and dispersion curves, thus obtaining the Rayleigh wave scattering, energy attenuation, distortion, and dispersion curve characteristics under different aggregate parameters. Based on the forward modeling data of different aggregate concrete models, this study quantitatively analyzed the sizes and influence ranges of aggregate-induced anomalies of the Rayleigh wave field and dispersion curves. The results are as follows. The randomness and content of aggregate could affect the energy attenuation of direct Rayleigh waves. The Rayleigh wave field was slightly influenced by the aggregate shape but significantly impacted by the aggregate size. When the aggregate size exceeded half of the dominant wavelength, Rayleigh waves would produce strong scattering, distorting its waveforms. In contrast, these aggregate parameters caused no anomalies in the dispersion curves. Therefore, data analysis using dispersion curves can avoid aggregate interference on the target in concrete quality detection by Rayleigh waves.

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Correction of the influence of mountains on grounded-source transient electromagnetic responses
ZHOU Zhong-Hang, ZHANG Ying-Ying
Geophysical and Geochemical Exploration    2023, 47 (5): 1236-1249.   DOI: 10.11720/wtyht.2023.1489
Abstract147)   HTML1)    PDF (5591KB)(239)      

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.

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Characterization of multi-attitude fractures in tight sandstones in the Yuanba area, northeastern Sichuan Basin
HUANG Yan-Qing
Geophysical and Geochemical Exploration    2023, 47 (5): 1189-1197.   DOI: 10.11720/wtyht.2023.1352
Abstract144)   HTML3)    PDF (9055KB)(169)      

This study proposed a fracture prediction method based on unsupervised clustering of fracture sensitivity attributes to accurately characterize the distribution of fractures with different attitudes in tight sandstones of the Upper Triassic Xujiahe formation in the Yuanba area, northeastern Sichuan. First, the sensitivity of fractures was extracted and selected based on the optimized post-stack seismic data. Then, the convolutional neural network, a deep learning algorithm, was used to learn global massive fault and fracture databases of various types, obtaining the intensities, dip angles, and azimuths of fractures. In combination with high-precision-guided curvature attributes, an unsupervised clustering algorithm based on the Bayesian probability model was used to predict the intensities of fractures with different dip angles through dimensionality reduction using principal component analysis (PCA). The prediction results are highly consistent with both the fracture interpretation results from imaging logs and the geological results. The results of this study show that the third member of the Xujiahe Formation has more developed fractures than the second member. Fractures in the third member include both the fault-induced fractures distributed near the faults in the southeast flank of the Jiulongshan anticline and the fold-induced fractures in the areas with large formation flexures. By contrast, only fault-induced fractures near the faults occur in the second member.

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GIS-based assessment of the radioactivity levels and risks of soil environment
QUE Ze-Sheng, LI Guan-Chao, HU Ying, JIAN Rui-Min, LIU Bing
Geophysical and Geochemical Exploration    2023, 47 (5): 1336-1347.   DOI: 10.11720/wtyht.2023.1582
Abstract143)   HTML1)    PDF (9237KB)(165)      

Investigating the concentrations of natural radionuclides in soils is basic for soil pollution prevention and control. First, this study determined the background values and anomaly thresholds of radionuclides 238U, 226Ra, 232Th, and 40K in soils in Guangdong Province using the geographic information system (GIS) and three methods, namely conventional statistics, exploratory data analysis (EDA), and median absolute deviation (MAD). Then, this study assessed the radioactivity levels of the soil environment using four indices: the γ radiation dose rate, the equivalent radium specific activity, the external exposure index, and the annual effective dose rate. Finally, this study assessed the health risks of the soil radioactivity using the geoaccumulation index method, the single factor index method, and the Nemerow composite index method. The results indicate that: (1) Radionuclides 238U, 226Ra, 232Th, and 40K in soils of Guangdong Province have average concentrations of 79.4, 102.95, 74.59, and 541.25 (Bq·kg-1·dry), respectively; (2) The four radionuclides have background values of 34.27、46.75、32.87 and 271.79 (Bq·kg-1·dry), and the anomaly values of 111.35、141.805、105.12、946.26 (Bq·kg-1·dry); (3) The radioactivity level indices for soil environment, namely D, Raeq, Hex, and AEDR, show averages of 121.44 ± 67.08 nGy/h, 263.48 ± 147.72 Bq/kg, 0.08~2.3, and 148.93 ± 82.26 μSv/a, respectively; (4) The radionuclide geoaccumulation index suggests clean soils, the single factor index indicates slight pollution, and the Nemerow composite index of 0.22~5.52 (average: 1.74 ± 0.97) indicates mild pollution. These three indices, which suggest roughly consistent results for the health risk assessment of radionuclides in soils, can serve as a supplement to the health risk assessment method for soil radioactivity.

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Research on time-frequency electromagnetic method detection of Wumishan Formation thermal reservoir in deep Xiong’an New Area
Cheng Zheng-Pu, Lian Sheng, Wei Qiang, Hu Wen-Guang, Lei Ming, Li Shu
Geophysical and Geochemical Exploration    2023, 47 (6): 1400-1409.   DOI: 10.11720/wtyht.2023.1611
Abstract143)   HTML8)    PDF (2331KB)(257)      

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.

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Geophysical characteristics and deep prospecting prediction of the Dachaigou gold deposit in the eastern Kunlun area
YU Zhong-Hong, YAN Ling-Qin, ZHANG Zhan-Xiong, LI Peng, LI Feng-Ting, FU Jia
Geophysical and Geochemical Exploration    2024, 48 (1): 40-47.   DOI: 10.11720/wtyht.2024.1126
Abstract139)   HTML5)    PDF (7232KB)(281)      

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.

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Application of the minimum entropy method based on a velocity-controlled moving window to the reverse time migration of ground-penetrating radars
XI Yu-He, WANG Hong-Hua, WANG Yu-Cheng, WU Qi-Ming
Geophysical and Geochemical Exploration    2023, 47 (5): 1250-1260.   DOI: 10.11720/wtyht.2023.1556
Abstract137)   HTML1)    PDF (6342KB)(196)      

Velocity is a key parameter determining the migration imaging resolution of ground penetrating radars (GPR).The method combining minimum image entropy and migration usually estimates the medium velocity by calculating the entropy curves using the overall migration profile as a fixed window.Therefore,such a method is not applicable to non-uniformly distributed media.Moreover,for this method,a too-high or too-low test velocity will make the convergence position of hyperbolic diffracted waves go beyond the fixed window,thus reducing the estimation accuracy.This study proposed a minimum entropy method based on a velocity-controlled moving window,in which the calculation window in the migration profile is accurately controlled by the test velocity.Then,this method was combined with inverse time migration to estimate the optimal migration velocity.By automatically adjusting the position of the calculation window using the trial velocity,this method keeps the convergence position of hyperbolic diffracted waves at the center of the calculation window.In this manner,stable and accurate entropy curves can be obtained.By comparing the calculation results with those of the minimum entropy method based on a fixed window,this study verified the correctness and effectiveness of the minimum entropy method based on a velocity-controlled moving window for a typical hyperbolic diffracted wave.As revealed by numerical experiments and the tests of measured data,compared with the minimum entropy method based on a fixed window,the minimum entropy method based on a velocity-controlled moving window can keep the convergence position of hyperbolic diffracted waves accurately at the center of the calculation window,yielding more stable entropy curves,lower computational complexity,higher estimation accuracy of the migration velocity,and better imaging performance of reverse time migration.

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Geological characteristics and origin of the Mogou fluorite deposit in Fangcheng County, Henan Province
ZHANG Qing-Song, XIA Ming-Zhe, WANG Chun-Lian, LI Ke-Kun, LIU Zeng-Zheng, JIANG Ji-Yong, JIANG Jian-Lang
Geophysical and Geochemical Exploration    2024, 48 (1): 15-23.   DOI: 10.11720/wtyht.2024.2588
Abstract136)   HTML6)    PDF (6964KB)(162)      

The Mogou fluorite deposit of Fangcheng County, residing in the Neoproterozoic Meiyaogou Formation, is a crucial part of the fluorite metallogenic belt in southern Henan Province. Based on the analysis of the geological characteristics of the Mogou fluorite deposit, this study conducted petrographic and petrogeochemical studies to define the source of ore-forming materials and probe into the genetic mechanism of the fluorite deposit. The results show that the fluorite ore body is veined or lenticular, with mineralization-related alterations composed of silicification, fluorite and sericite alterations. Its ore structures are primarily massive, followed by banded, striped, and brecciated types. The chondrite-normalized rare earth element distribution pattern of the fluorite ore body is similar to that of the Meiyaogou Formation marbles and the Yanshanian porphyritic plagiogranites, suggesting a genetic relationship. The possible genetic mechanism is that the F-enriched ore-bearing hydrothermal liquids intruded along the interbedded fault and reacted with the surrounding rocks to form the fluorite ore /mineralized body. The deposit belongs to the epithermal filling type along the interbedded structure.

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Delineation of areas with high geological background values of heavy metals in soils in Yunnan Province, China based on geological big data technology
XIAO Gao-Qiang, ZHAO Juan, CHEN Zi-Wan, SONG Xu-Feng, ZHU Neng-Gang
Geophysical and Geochemical Exploration    2024, 48 (1): 216-227.   DOI: 10.11720/wtyht.2024.1129
Abstract134)   HTML3)    PDF (4168KB)(162)      

This study aims to systematically investigate the distribution and over-limit elements of areas with high geological background values of heavy metals in soils in Yunnan Province. GIS spatial analysis was conducted based on the heavy metal content data from a province-wide 1∶200,000 stream sediment survey and the regional geological map. The analysis results were validated using the data of heavy metals in soils in Kunming, Yuxi, Zhaotong, and other regions. A total of 61 geological units were identified, with heavy metal content in soils exceeding the screening values of agricultural land, accounting for 21.09% of the total land area of Yunnan. The cultivated land in high geological background areas covers an area of approximately 2.844 1 million hectares, accounting for 7.22% of the total land area of Yunnan. The lithologies that cause over-limit heavy metals in soils primarily comprise carbonate rocks, mafic-ultramafic volcanic rocks, intermediate mafic intrusive rocks, coal-bearing clastic rocks, and clastic rocks with mafic components. The over-limit heavy metal elements in high geological background areas are dominated by Cu, Cr, Ni, and Cd. In contrast, As manifests an over-limit risk mainly in carbonate rock formations, Pb and Zn only exhibit an over-limit risk in individual strata, and Hg almost shows no over-limit risk.

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Research on the application of the integrated gravity-magnetic-radioactive geophysical exploration method in the exploration of rare earth deposit in Weishan, western Shandong
LAN Jun, LI Zhao-Ling, ZHANG Peng, LI Zhi-Min, LI De-Jian, XING Nan, SUN Li, YANG Yun-Tao, XU Hong-Yan, WANG Jian, WANG Qiao-Yun
Geophysical and Geochemical Exploration    2023, 47 (6): 1417-1424.   DOI: 10.11720/wtyht.2023.0189
Abstract133)   HTML8)    PDF (4793KB)(251)      

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.

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Three-dimensional imaging based on the ultrasonic planar array-total focusing method
ZHANG Bang
Geophysical and Geochemical Exploration    2023, 47 (5): 1273-1280.   DOI: 10.11720/wtyht.2023.1414
Abstract131)   HTML0)    PDF (3504KB)(211)      

Given large data volumes and low post-processing efficiency of full matrix capture-total focusing imaging,this study proposed a planar array-total focusing method(PATFM) for the imaging of planar array data.First,the wave front time of the downgoing planar array was calculated using the eikonal equation based on the characteristics of both the total focusing imaging algorithm and the planar array wave field.Then,the total focusing imaging formula was improved using the upgoing and downgoing ultrasonic propagation time based on the delay superposition principle.Finally,focusing imaging was performed on a wide range of imaging points below the planar array aiming at the derived directivity and diffusion correction coefficient of the planar array.Through Field II simulation,the PATFM was compared with three imaging methods,including phase-controlled scanning imaging,full matrix capture-based total focusing imaging,and plane wave capture-based total focusing imaging.The results show that the PATFM can be used for large-range focusing imaging of single planar array data,greatly improving the computational efficiency while obtaining corresponding accuracy.Therefore,this study provides a feasible technical means for 3D imaging of array acoustic waves.

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Geochemical characteristics of fluorine in irrigation water and soils in the Gaomi area, Shandong Province, China
JIANG Bing, LIU Yang, WU Zhen, ZHANG De-Ming, SUN Zeng-Bing, MA Jian
Geophysical and Geochemical Exploration    2023, 47 (5): 1348-1353.   DOI: 10.11720/wtyht.2023.1527
Abstract131)   HTML0)    PDF (1766KB)(219)      

This study aims to ascertain the distribution patterns and influencing factors of fluorine in irrigation water and soils in the Gaomi area, Shandong Province, China. Through systematic sampling and testing, this study obtained data including the pH and fluoride concentration of irrigation water and the pH, organic matter, and fluorine concentration of soils. Based on these data, this study plotted the geochemical contour maps for statistical, correlation, and difference analyses. Furthermore, this study explored the influencing factors. The results are as follows: (1) The irrigation water in the study area has a fluoride concentration of 1.89 mg/L on average, which shows strong spatial variability. Zones with high fluoride concentrations in irrigation water are distributed in the northern low-flat alluvial plain, with the number of samples with fluoride concentrations greater than 2 mg/L accounting for 63.16%. There is a significant positive correlation between the fluoride concentration in the irrigation water and the pH (P < 0.01); (2) The soils have a fluoride concentration of 455×10-6 on average, which shows an inhomogeneous spatial distribution. Zones with high or excess fluorine concentrations are distributed in the northern part of the study area. The fluorine concentrations of soils show significant positive correlations with the pH and organic matter of soils and the fluoride concentration of irrigation water (P < 0.01); (3) The fluoride concentrations in the irrigation water and soils are high in the distribution area of lime concretion black soil. The results of this study reveal the background characteristics and influencing factors of fluoride in the irrigation water and soils of the Gaomi area, providing a geochemical basis for the precise prevention and control of endemic fluorosis.

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Two-dimensional joint inversion based on the marine controlled-source electromagnetic method and seismic full-waveform
KONG Fan-Xiang, TAN Han-Dong, LIU Jian-Xun
Geophysical and Geochemical Exploration    2024, 48 (1): 67-76.   DOI: 10.11720/wtyht.2024.2583
Abstract127)   HTML1)    PDF (5740KB)(136)      

To reduce the limitations and the multiplicity of solutions of a single geophysical inversion method, this study investigated the two-dimensional joint inversion based on the marine controlled-source electromagnetic (MCSEM) method and seismic full-waveform inversion. The MCSEM method employs the data-space Occam’s algorithm, while the seismic full-waveform inversion utilizes the gradient algorithm. By incorporating a cross-gradient function for the mutual coupling of the two types of physical property parameters, this study developed a two-dimensional joint inversion method, whose accuracy was verified using three different models. As indicated by the results, compared to a single inversion method, the MCSEM-based joint inversion yielded significantly improved inversion results, predominantly in terms of the morphology characterization of anomalous bodies, as well as the reconstruction of their structure and textures and their physical property values. Therefore, the full-waveform inversion can enhance the reliability of the MCSEM inversion results.

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Neural network-based denoising for ground-penetrating radar data
WU Song, NING Xiao-Bin, YANG Ting-Wei, JIANG Hong-Liang, LU Chao-Bo, SU Yu-Di
Geophysical and Geochemical Exploration    2023, 47 (5): 1298-1306.   DOI: 10.11720/wtyht.2023.1347
Abstract127)   HTML1)    PDF (6256KB)(231)      

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.

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An integrated data quality evaluation of Earth magnetic anomaly grid EMAG2v3 and global gravimetric database V29: A case study of the Aegir ridge in the Arctic
ZHANG Mian, ZHANG Chun-Guan, ZHAO Min, ZHONG Zhen-Hua, YUAN Bing-Qiang, ZHOU Lei, HAN Mei
Geophysical and Geochemical Exploration    2023, 47 (6): 1410-1416.   DOI: 10.11720/wtyht.2023.1558
Abstract124)   HTML5)    PDF (3654KB)(139)      

To evaluate the qualities of the marine magnetic data in the Earth magnetic anomaly grid EMAG2v3 and the marine gravity data in global gravimetric database V29, this study selected the magnetic and gravity data of the Aegir axial rift and its adjacent areas within a range of about 150 km from EMAG2v3 and V29, respectively to conduct comparative research. This study systematically collected the anomaly data of the study area from EMAG2v3 and V29 for comparison with the measured gravity and magnetic data of the study area. First, this study gridded and whitened the EMAG2v3 data, V29 data, and measured gravity and magnetic anomaly data to obtain the corresponding images. Then, this study analyzed the correlations between the EMAG2v3 data and the shipborne magnetic data and between the V29 data and the shipborne gravity data, obtaining the magnetic and gravity correlation diagrams and corresponding correlation coefficients. By comparing the correlation coefficients and differences between the two kinds of magnetic data and the two kinds of gravity data, this study conducted an integrated evaluation of magnetic the gravity data of the study area from EMAG2v3 and V29, respectively. As indicated by the results, EMAG2v3 incorporates many shipborne magnetic data, with the shipborne magnetic anomaly data showing higher quality than the data from the EMAG2v3 for areas with dense survey lines. The results also show that the shipborne gravity anomalies showed roughly the same variations as those from V29, indicating the same lateral resolution of the two types of anomaly data.

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Heavy metal pollution and health risk assessment of groundwater in a typical chemical industry park in northwestern Shandong, China
FAN Hai-Yin, SONG Rui-Rui, YU Lin-Song, TENG Yong-Bo, WAN Fang, ZHANG Xiu-Wen, LI Sheng-Yu, ZHAO Chuang
Geophysical and Geochemical Exploration    2023, 47 (5): 1326-1335.   DOI: 10.11720/wtyht.2023.1367
Abstract123)   HTML2)    PDF (4861KB)(210)      

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.

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Fine-scale prospecting targets of skarn iron deposits in the Pandian gravity-magnetic anomaly zone of northwestern Shandong Province: Insights from deep prospecting using the wide-field electromagnetic method
GUO Guo-Qiang, LI Ya-Dong, WANG Yang, YU Jia-Bin, WANG Run-Sheng, GAO Xiao-Feng, ZHANG Da-Ming, HU Dong-Ning, FANG Lei, GUO Wei-Fang
Geophysical and Geochemical Exploration    2024, 48 (2): 327-333.   DOI: 10.11720/wtyht.2024.1157
Abstract122)   HTML3)    PDF (4258KB)(214)      

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.

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Multi-source frequency-domain seismic exploration technique and its application
SUN Hong-Lin, LIU Tie-Hua, LIU Tie, ZHANG Zhan-Rong, CHEN Zhi-Xing
Geophysical and Geochemical Exploration    2024, 48 (3): 618-628.   DOI: 10.11720/wtyht.2024.1317
Abstract122)   HTML3)    PDF (5836KB)(129)      

Due to various strong electromagnetic mechanical interference and traffic barriers, many geophysical exploration techniques are ineffective in urban geophysical exploration.Based on transient surface waves,microtremor arrays,and microtremor spectral ratios,this study synthetically extracted two kinds of characteristic curves for joint inversion from the multi-source frequency-domain seismic data obtained by multi-point three-component low-frequency sensors.Consequently,this study achieved multi-source frequency-domain seismic exploration that integrated three techniques and developed the two-source synthetic dispersive spectrum extraction technique,the two-source characteristic curve joint inversion technique,and the equivalent homogeneous medium forward modeling technique based on inhomogeneous media.Engineering practice results demonstrate the improvements in the exploration accuracy and efficiency.

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Critical processing techniques for ocean bottom node data of the diapir fuzzy zone of the Dongfang 1-1 structure and their application
ZHANG Min, DENG Dun, LI San-Fu, SHI Wen-Ying, ZHANG Xing-Yan, ZHI Ling
Geophysical and Geochemical Exploration    2023, 47 (6): 1456-1466.   DOI: 10.11720/wtyht.2023.0006
Abstract120)   HTML3)    PDF (13508KB)(196)      

The Dongfang 1-1 structure is situated in the northern part of the central mud diapir tectonic belt of the Yinggehai Basin on the northern continental shelf of the South China Sea.The Dongfang 1-1 gas field is the first uncompartmentalized shallow gas field discovered in the Yinggehai Basin.Despite abundant oil and gas reserves in this region, the imaging of the diapir fuzzy zone has been a critical factor restricting oil and gas exploration in this region.The original streamer-based seismic data,through multiple rounds of multi-company reprocessing,still failed to effectively image the diapir fuzzy zone.Therefore,the second acquisition of three-dimensional ocean bottom node(OBN) seismic data was conducted in this region.According to the geological conditions and the characteristics of OBN data in this region,this study proposed several critical processing techniques,including OBN preprocessing,multi-component joint shear-wave noise suppression,wavelet-domain dual-sensor summation,and full-waveform-inversion(FWI) high-precision velocity modeling.These techniques effectively improved the imaging of shallow fault structures and middle and deep diapir fuzzy zones,thus providing reliable fundamental data for the subsequent target evaluation.

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Sulfur isotopic composition and related issues of typical gold ore districts in China
LAN Rui-Xuan, ZHAO Hong-Kun, TANG Shi-Xin, DUAN Zhuang, MA Sheng-Ming
Geophysical and Geochemical Exploration    2024, 48 (2): 296-313.   DOI: 10.11720/wtyht.2024.1177
Abstract115)   HTML9)    PDF (5941KB)(154)      

In the Prospecting Breakthrough Strategy (2011~2020), China has made significant progress in the exploration of gold deposits, demonstrating considerable prospecting potential. Element sulfur, a mineralizer, is closely associated with the formation of gold deposits, proved to be the most significant element in gold deposit formation by scholars at home and abroad. Sulfur isotopes have been extensively used to trace the sources of minerals in gold deposits. Different gold deposits reside in distinct geological settings. Since sulfur isotopic compositions are governed by various sulfur sources, sulfur isotopes in gold deposits can reflect the geological settings of mineralization. The ore-district-scale spatio-temporal distribution of sulfur isotopes has theoretical implications, playing a significant role in guiding ore prospecting. The gold resources in China are distributed in 42 gold ore districts, typified by Jiaodong, Xiaoqinling, and Yunnan-Guizhou-Guangxi. This study comparatively analyzed and summarized the characteristics of sulfur isotopes in the three typical gold ore districts, providing theoretical and methodological support for future gold prospecting.

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Distributions of the total concentration, bioavailability, and speciation of selenium in soils in Luoyang City, Henan Province, China
TIAN Qiang-Guo, HOU Jin-Kai, YANG Zai-Wei, LI Li-Yuan
Geophysical and Geochemical Exploration    2023, 47 (5): 1371-1378.   DOI: 10.11720/wtyht.2023.1488
Abstract111)   HTML2)    PDF (2826KB)(172)      

Targeting the selenium resource in soils of Luoyang City, Henan Province, this study analyzed the distribution of total selenium concentration under different geological settings, soil types, land use types, acidity and alkalinity, and organic matter. Furthermore, it determined the bioavailability and speciation distribution of selenium in the soils. The results indicate that: (1) The soils in Luoyang City have total selenium concentrations of (0.03~5.67)×10-6, with an average of 0.30×10-6, and the area of soils with moderate and rich selenium accounts for 94.73%; (2) The average selenium concentration is the highest in soils of the Jixian Yunmengshan formation and the lowest in soils of the Cambrian Xinji Formation; (3) The average total selenium concentration is the highest in lime concretion black soil and the lowest in paddy soil; (4) Regarding land use types, the average total selenium concentration is relatively high in soils of paddy land and woodland; (5) Soils with high acidity and high organic matter concentrations are favorable for selenium enrichment; (6) In terms of soil types, the average concentration of bioavailable selenium is the highest in fluvo-aquic soils and the lowest in red clays; (7) The average concentration of bioavailable selenium is higher in alkaline soils than in neutral and acidic soils; (8) Selenium in soils primarily occurs in residue, strong organic bound, and humic acidic bound forms, with the highest average concentration of bioavailable selenium occurring in alkaline soils and red clays. The selenium resource in the soils in Luoyang City has high utilization potential, and it is feasible to conduct targeted development and planning of the selenium-rich industry according to the distribution of total selenium concentration in the study area.

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Research on the detection of underground pedestrian passage by high precision gravity exploration
YANG Min, XU Xin-Qiang, CHEN Ming, Ji Xiao-Lin, WANG Wan-Yin, ZHAO Dong-Ming, ZHOU Wei, ZHANG Yi-Mi
Geophysical and Geochemical Exploration    2024, 48 (3): 876-883.   DOI: 10.11720/wtyht.2024.0047
Abstract111)   HTML8)    PDF (3819KB)(123)      

Underground cavities with shallow burial and small scale are difficult to detect. With the development of gravity sensing technology, the accurate and rapid acquisition of micro-gravity variations brings new opportunities for detecting underground cavities, and it has wide research and practical value for the detection of small-scale underground cavities. This paper systematically analyzes and studies underground cavities from three aspects: gravity basic theory, gravity detection technology, and gravity data processing and inversion. Under given body size and gravity data accuracy, the maximum burial depth of gravity detection is calculated using the bisection method. High-density acquisition and high-precision gravity detection methods are applied to the actual detection of an underground pedestrian tunnel in a certain area of a passenger station. A set of high-precision gravity grid data is obtained. The theoretical research and measurement results indicate that existing gravity instruments have the ability to detect underground cavities. By using the minimum curvature potential field separation method, 2.5D interactive inversion and the target area recognition three-dimensional physical property fast inversion method, the approximate SN distribution and burial depth of the underground pedestrian tunnel are obtained, which is approximately 2.5~5 m, consistent with the actual situation. This study has developed a complete gravity exploration process for detecting underground cavities, and it has certain reference value.

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Bayesian prestack seismic stochastic inversion based on the exact Zoeppritz equation
NIU Li-Ping, HU Hua-Feng, ZHOU Dan, ZHENG Xiao-Dong, GENG Jian-Hua
Geophysical and Geochemical Exploration    2024, 48 (1): 77-87.   DOI: 10.11720/wtyht.2024.2572
Abstract110)   HTML2)    PDF (8080KB)(134)      

The prestack seismic inversion method based on the exact Zoeppritz equation is challenged by seismic data with low signal-to-noise ratios(SNRs).The Markov chain Monte Carlo(MCMC) simulation is a heuristic global optimization algorithm that can achieve effective prestack nonlinear inversion of elastic parameters.The conventional MCMC-based prestack inversion method,which characterizes the statistical properties of elastic parameters via the Gaussian distribution,has significant limitations when applied to complex lithologic reservoirs.Besides,due to the influence of the huge parameter space of subsurface models and the noise in seismic data,the MCMC search process for the posterior probability distribution of elastic parameters is very sensitive to local extrema,making it difficult to obtain stable and accurate results from MCMC-based prestack inversion.This study proposed an improved MCMC-based elastic parameter inversion method to address the challenges faced by the prestack inversion based on the exact Zoeppritz equation under the conditions of actual complex reservoirs and seismic data with low SNRs.First,the method reduced the complexity of the posterior probability distribution by transforming the parameters to be inverted into the perturbations of the model parameters using a low-frequency model (LFM) constraint.Then,the seismic forward modeling process was constrained by taking the logarithm of the likelihood function and utilizing an LFM.Finally,a multi-chain algorithm based on random subspace sampling was employed to perform global optimization for the prestack nonlinear inversion problems,thus avoiding premature convergence of the sampling process to local extrema.As indicated by the tests on the simulated data with low SNRs and the actual data,the method proposed in this study can yield more accurate and stable inversion results while providing credible and quantitative uncertainty estimates for the inversion results.

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Petrogenesis and rubidium enrichment indication of the Fuling rock mass in southern Anhui Province
ZHANG Jun, TAO Nai, QI Shang-Xing, WANG Zhi-Qiang, DA Hao-Xiang
Geophysical and Geochemical Exploration    2024, 48 (3): 584-596.   DOI: 10.11720/wtyht.2024.1268
Abstract109)   HTML8)    PDF (7620KB)(88)      

The Fuling rock mass in southern Anhui Province, located in the eastern section of the Jiangnan uplift zone, is a complex granitic rock mass that has experienced multi-stage evolution. It primarily comprises two lithologies: Monzogranite and K-feldspar granite. By investigating the geological, petrographic, and petrogeochemical characteristics of the Fuling rock mass, this study delved into its evolutionary characteristics, genetic types, and tectonic environment, aiming to clarify its indication significance for rubidium enrichment. The results of this study are as follows: ① The geochemical characteristics of the Fuling rock mass demonstrate high SiO2, Na2O, K2O, and Al2O3 contents, high w(K2O)/w(Na2O) ratios, and aluminum saturation indices (A/CNK) ranging from 0.95~1.08 (average: 0.99), suggesting high-K calc-alkaline quasi-aluminous to peraluminous granites; ② In terms of trace elements, the Fuling rock mass possesses high Li, Rb, Nd, and Ta contents and significantly low Sr and Ba contents, which may be associated with the fractional crystallization of feldspar; ③ The w(Nb)/w(Ta) ratios ranging from 5.71~10.94 (average: 8.41) and Mg# values ranging from 0.02~0.31 (average: 0.13) indicate that the Fuling rock mass was primarily derived from the partial melting of lower crust rocks, suggesting A-type granites in a non-orogenic extensional environment; ④ The Rb content in the Fuling rock mass increases with the magmatic evolution degree. Compared to monzogranites, K-feldspar granites with a higher evolution degree display higher Rb content, implying that the Rb content in the Fuling rock mass is generally controlled by magmatic evolution. Overall, this study holds some reference significance for understanding the Yanshanian diagenesis and mineralization of southern Anhui Province.

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Application of natural thermoluminescence measurement technique in natural gas hydrate exploration in permafrost areas
WANG Hui-Yan, TANG Rui-Ling, BI Jing
Geophysical and Geochemical Exploration    2024, 48 (1): 24-30.   DOI: 10.11720/wtyht.2024.1037
Abstract107)   HTML5)    PDF (2704KB)(152)      

Since natural gas hydrates (NGHs) in permafrost areas feature complex formation mechanisms and multiple sources, there is an urgent need to develop multiple techniques for micro-leakage information capture in order to increase the exploration success rate. This study applied the natural thermoluminescence measurement technique to NGH exploration in a permafrost area for the first time. Specifically, it tested the thermoluminescence intensity in soil samples from the Muli permafrost area of the Qilian Mountains using an RGD-6 thermoluminescent dosimeter. Then, it summarized the heating procedure for NGH exploration in the area, as well as size fractions for sampling. The results show that the soil samples from the Muli permafrost area demonstrated optimal size fractions for sampling ranging from -60~100 meshes, an optimal heating rate of 5 ℃/s, and an optimal heating range of 50~400 ℃. Based on the anomaly characteristics of the natural thermoluminescence intensity in soil samples, this study determined the anomaly boundary of NGHs on the surface of the permafrost area. It revealed that the natural thermoluminescence intensity displayed anomalies on the top, which correspond well to the hydrocarbon anomaly mode. The natural thermoluminescence measurements of soil, unaffected by microorganisms and boasting high sensitivity, can be popularized as a promising method for NGH explorations in permafrost areas.

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Application of supervised descent method for 2D magnetotelluric inversion and its application
FU Xing, TAN Han-Dong, DONG Yan, WANG Mao
Geophysical and Geochemical Exploration    2024, 48 (1): 175-184.   DOI: 10.11720/wtyht.2024.1417
Abstract106)   HTML1)    PDF (5394KB)(153)      

Traditional two-dimensional inversion methods of magnetotelluric are mature, but there are still some problems, such as reliance on the initial model, reliance on regularization parameter selection, and easy to fall into local minimum. In order to solve the above problems, this paper adopts the supervised descent method to improve the effect of two-dimensional inversion of magnetotelluric. The supervised descent method is a machine learning algorithm that learns the average descending direction to predict the residual of data. Based on the theory of supervised descent method, this paper develops the two-dimensional inversion algorithm of magnetotelluric, designs the theoretical model synthesis example to verify the correctness of the algorithm, and inverts the measured data on the Tibet Plateau to test the practicability of the supervised descent method. The inversion results of the theoretical model synthesis data and the measured data show that, compared with the traditional nonlinear conjugate gradient inversion, the inversion based on the supervised descent method has the characteristics of fast convergence speed, good inversion effect, and strong anti-noise ability.

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