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Gravity field characteristics and boundaries of geotectonic units on the northeastern margin of the Linyi uplift, Shandong Province
WANG Run-Sheng, WU Bin, ZHANG Hai-Rui, YU Jia-Bin, DONG Yan-Long, GUO Guo-Qiang, KANG Yi-Ming
Geophysical and Geochemical Exploration    2023, 47 (2): 279-289.   DOI: 10.11720/wtyht.2023.1144
Abstract783)   HTML25)    PDF (9602KB)(494)      

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

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Progress and prospect of gravity and magnetic techniques for hydrocarbon exploration in China
LIU Yun-Xiang, SI Hua-Lu, QIAO Hai-Yan, LIU Bai-Chuan
Geophysical and Geochemical Exploration    2023, 47 (3): 563-574.   DOI: 10.11720/wtyht.2023.1484
Abstract513)   HTML344)    PDF (3583KB)(362)      

This study summarized the progress and major application performance of gravity and magnetic techniques for onshore hydrocarbon exploration in China in recent years.By combining the research results of the authors,this study elucidated the new progress made in the gravity and magnetic techniques for hydrocarbon exploration from the prospect of acquisition,processing,interpretation,and application and sorted the application performance of these techniques in key fields including deep targets,complex areas,and volcanic rocks.Moreover,this study future analyzed the demand for the gravity and magnetic techniques for hydrocarbon exploration.By combining the new trends of gravity and magnetic exploration techniques at home and abroad,this study proposed the development direction and application prospect of gravity and magnetic techniques for oil and gas in deep strata and igneous rocks in complex areas.The results of this study show that significant progress has been made in gravity and magnetic exploration techniques,which play an important role in supporting the current hydrocarbon exploration.It is expected to develop high-precision and high-density gravity and magnetic exploration techniques and gravity-gravity-electricity-seismic collaborative innovation techniques.

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Application of a comprehensive geophysical exploration methods in the exploration of geothermal resources in Yueliangwan, Binhai County
WANG Jun-Cheng, ZHAO Zhen-Guo, GAO Shi-Yin, LUO Chuan-Gen, LI Lin, XU Ming-Zuan, LI Yong, YUAN Guo-Jing
Geophysical and Geochemical Exploration    2023, 47 (2): 321-330.   DOI: 10.11720/wtyht.2023.1205
Abstract302)   HTML10)    PDF (6825KB)(377)      

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

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Seismic characteristics of the paleo-underground river system in Ordovician carbonate paleo-buried hills in the western Lungu area
DAN Guang-Jian, ZHOU Cheng-Gang, LIU Yun-Hong, LI Xiang-Wen, ZHANG Liang-Liang, ZHANG Ming, WANG Chun-Yang
Geophysical and Geochemical Exploration    2023, 47 (2): 290-299.   DOI: 10.11720/wtyht.2023.1052
Abstract294)   HTML16)    PDF (8684KB)(231)      

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

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Research on edge depth inversion of 2D geological body based on gravity and magnetic field
WANG Wan-Yin, LUO Xin-Gang
Geophysical and Geochemical Exploration    2023, 47 (3): 547-562.   DOI: 10.11720/wtyht.2023.1464
Abstract284)   HTML383)    PDF (8058KB)(427)      

The edge depth of geological body plays a crucial role in the semi-quantitative interpretation of gravity and magnetic potential field exploration. At present, the main inversion methods of geological body edge depth mainly include Werner deconvolution method, analytical signal amplitude method, local wave number method, Tilt-depth method, Euler deconvolution method and curvature attribute inversion method. These methods all have problems of solution selection, stability and adaptability. This paper mainly studies the adaptability of different types of data and models. Through basic principle analysis and model test, the results show that Werner deconvolution method and Euler deconvolution method are applicable to the most types of data sources, followed by curvature attribute, and Tilt-depth is the least; Werner deconvolution method, Euler deconvolution method and curvature attribute methods can adapt to many models, the Tilt-depth is least. For gravity data, the analytical signal amplitude of the first vertical derivative as the data source is applicable to all methods. For magnetic data, the analytical signal amplitude as data source is applicable to all methods. At the same time, it is suggested that other scholars should follow the following principles when using these methods to invert the edge depth of the two-dimensional body: It is recommended that Werner deconvolution is preferred, followed by curvature attribute and Euler deconvolution. The gravity data source of Werner deconvolution method and Euler deconvolution method is recommended to use the horizontal derivative of the first vertical derivative, and the magnetic data source is recommended to use the horizontal derivative. The gravity data source of curvature attribute method is recommended to use the analytical signal amplitude of the first vertical derivative, and the magnetic data source is recommended to use the analytical signal amplitude. In addition, based on the above research conclusions, some suggestions on the future research directions of the solution screening, stability and adaptability of the edge depth inversion are given.

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Application of shallow drilling geochemical survey to shallow overburden area at the peripheral of Nanjinshan gold mine in Beishan, Gansu Province
WEI Zhen-Hong, ZHAO Ji-Chang, QU Zheng-Gang, FAN Xin-Xiang, LI Sheng-Ye, CHEN Hai-Yun, LIU Yong-Biao, YANG Zhen-Xi
Geophysical and Geochemical Exploration    2023, 47 (2): 331-342.   DOI: 10.11720/wtyht.2023.1192
Abstract248)   HTML3)    PDF (8368KB)(236)      

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

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Application of integrated geophysical methods in deep ore prospecting of Laochang polymetallic mining area in Lancang, Yunnan
YOU Yue-Xin, DENG Ju-Zhi, CHEN Hui, YU Hui, GAO Ke-Ning
Geophysical and Geochemical Exploration    2023, 47 (3): 638-647.   DOI: 10.11720/wtyht.2023.1578
Abstract239)   HTML20)    PDF (6931KB)(346)      

Laochang, Lancang, Yunnan is one of the most important polymetallic mining areas in the southern part of Sanjiang Tethys metallogenic belt. After years of mining, the shallow resources are nearly exhausted. In recent years, granite porphyry and porphyry polymetallic mineralization have been newly discovered in the deep part of the mining area, highlighting the prospecting potential of deep polymetallic deposits. In order to trace the occurrence of deep ore-controlling strata and structures in the study area and help to make a breakthrough in deep ore prospecting, high-power induced polarization method and audio magnetotelluric method were implemented to image the deep structure situated. Results obtained from the inversion of the measured induced polarization and electromagnetic data recuperated the distribution of induced polarization anomalies and the characteristics of deep electrical structure within the study area. Combined with the available regional geological settings, the main conclusions are as follows: The low resistance and high polarization anomalies in the northwest of the survey area are deeply related to the surface ferromanganese, silver manganese, and deep polymetallic mineralization, and the high resistance and high polarization anomalies in the middle and east of the survey area are in good agreement with the deep polymetallic mineralization. The upper Carboniferous limestone and dolomite strata are thick in the west and thin in the east, with the west strata dipping to SW and the east strata overlying the Yiliu Formation of the lower Carboniferous. The concealed granite porphyry dips in NE direction, and the coupling part between its deep 2 300~2 800 m horizontal section and deep fault is a favorable area for deep polymetallic mineralization. Notably, joint interpretation yielded from the high-power induced polarization method and the audio magnetotelluric method applied improved the reliability of deep polymetallic ore detection and provided more information of positioning the subsequent drilling layout.

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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
Abstract232)   HTML16)    PDF (4903KB)(167)      

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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Application of the opposing coils transient electromagnetic method in investigation of mined-out areas of a gold deposit
REN Xi-Rong, LI Xin, ZHOU Zhi-Jie
Geophysical and Geochemical Exploration    2023, 47 (2): 540-546.   DOI: 10.11720/wtyht.2023.1225
Abstract226)   HTML6)    PDF (5274KB)(339)      

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

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Fluid inclusions and formation mechanisms of the Dongjianian silver deposit in Lingbao City, Henan Province, China
LIU Chang, ZHANG Can-Hui, ZHANG Xin, ZONG Rui
Geophysical and Geochemical Exploration    2023, 47 (2): 343-352.   DOI: 10.11720/wtyht.2023.1095
Abstract219)   HTML3)    PDF (7090KB)(139)      

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

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Surface geochemical anomalies of concealed volcanic hydrothermal uranium deposit in northern Hebei
ZHANG Yang-Yang, CHEN Yue-Long, LI Da-Peng, KANG Huan, FANG Ming-Liang, XU Yun-Liang
Geophysical and Geochemical Exploration    2023, 47 (2): 300-308.   DOI: 10.11720/wtyht.2023.2695
Abstract210)   HTML7)    PDF (2883KB)(226)      

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

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Karst exploration in urban complex environments based on electrical resistivity tomography: A case study of Beihuan New Village in Guigang City
QIN Jian-Wen, JIANG Xiao-Teng, XIE Gui-Cheng, SUN Han-Wu, HE Liu, SUN Huai-Feng
Geophysical and Geochemical Exploration    2023, 47 (2): 530-539.   DOI: 10.11720/wtyht.2023.1253
Abstract201)   HTML6)    PDF (10783KB)(298)      

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

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A review of the research progress and application status of seismic full waveform inversion
CHEN Zi-Long, WANG Hai-Yan, GUO Hua, WANG Guang-Wen, ZHAO Yu-Lian
Geophysical and Geochemical Exploration    2023, 47 (3): 628-637.   DOI: 10.11720/wtyht.2023.1469
Abstract193)   HTML14)    PDF (3181KB)(227)      

As resource exploration deepens and becomes increasingly difficult,improving the imaging precision and the reservoir prediction accuracy under a complex tectonic setting has become a top priority of research.The full waveform inversion (FWI) method developed in recent years can be applied to complex geological structures.This method can reveal structural details in a complex geological setting using the dynamic and kinematic information in the pre-stack seismic wave field.However,this method involves many research elements such as model parameterization,building of inverse error function,data preprocessing,numerical simulation of wavelengths,and wavelet estimation.Thus,its development is bound to be a long-term gradual improvement process.The FWI method has been applied to actual observation data with the development of theory and computer technology.This study introduced the principle and processing flow of the FWI method and summarized its development history and its application status in marine and onshore seismic data,and deep seismic reflection data.Accordingly, this study presented the current application bottlenecks,data processing difficulties, and challenges of deep-crustal inversion imaging for subsequent research and application of the FWI method.

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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
Abstract187)   HTML9)    PDF (14675KB)(175)      

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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The anomalies determined using a soil geochemical survey and prospecting model of the Matou gold deposit in Sichuan Province
LI Jun-Jun, WEI Yu, ZHANG Qing-Song, WANG Wei-Hua, LIU Wei, XIANG Liang
Geophysical and Geochemical Exploration    2023, 47 (2): 309-320.   DOI: 10.11720/wtyht.2023.2456
Abstract175)   HTML7)    PDF (4740KB)(249)      

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

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A real-time correction method based on time-varying zero offset for the equivalent sampling of ground penetrating radars
FENG Wen-Ya, CHENG Dan-Dan, WANG Cheng-Hao, CHENG Xing
Geophysical and Geochemical Exploration    2023, 47 (2): 372-376.   DOI: 10.11720/wtyht.2023.2657
Abstract172)   HTML3)    PDF (1781KB)(175)      

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

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Application of a comprehensive geophysical exploration methods to water exploration in magmatic rock mountainous areas with water shortage in Jiaodong Peninsula
LIU Chun-Wei, WANG Chong, HU Cai-Ping, SHI Yan-Fang, YANG Xiao-Hui, LIU Xiao-Tian, HAN Yu-Ying, LI Bo
Geophysical and Geochemical Exploration    2023, 47 (2): 512-522.   DOI: 10.11720/wtyht.2023.1319
Abstract169)   HTML3)    PDF (11619KB)(285)      

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

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Application of opposing-coils transient electromagnetics in the detection of landslide deposits
LUO Shu, CHEN Zheng-Yu, LAN Yu-Cheng, LIU Yang-Fei, DUAN Ming-Jie
Geophysical and Geochemical Exploration    2023, 47 (2): 523-529.   DOI: 10.11720/wtyht.2023.1152
Abstract166)   HTML6)    PDF (5088KB)(307)      

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

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An application study of the comprehensive geophysical prospecting method in the exploration of mineral water: A case study of the Langqiao area, Jing County
ZHANG Zhi, XU Hong-Miao, QIAN Jia-Zhong, XIE Jie, CHEN Hao-Long, ZHU Zi-Xang
Geophysical and Geochemical Exploration    2023, 47 (3): 690-699.   DOI: 10.11720/wtyht.2023.1443
Abstract166)   HTML15)    PDF (7344KB)(268)      

The area around Maduqiao Village, Langqiao Town, Jing County has great potential for the development of high-quality mineral water. However, due to the geological conditions and the inhomogeneity of water-bearing media, the investigation of the distribution range of the mineral water in the area and the quantitative evaluation of the water quantity and quality have always been challenges to the development and utilization of mineral water in the area. With the Langqiao area of Jing County as the target area, an application study on the comprehensive geophysical prospecting method that comprehensive ground geophysical prospecting with hydrogeological logs was conducted, achieving important progress. The major results are as follows: (1) The fault structures in granodiorites were precisely located through comprehensive ground geophysical prospecting, and the horizon of tectonic fissure water was precisely identified based on hydrogeological logs; (2) The metasilicate natural mineral water for drinking with a single well water yield of 50~80 m3/d was identified; (3) The water-rich fault structures in the study area have a medium to shallow burial depths of about 75~140 m and primarily have a NW strike. These results reveal the spatial distribution characteristics of the mineral water-bearing structures in the study area and are of great significance to the subsequent investigation of the mineral water range. Moreover, the systematic research philosophy and technical methods used for the Langqiao area of Jing County in this study can guide the mineral water exploration in similar 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
Abstract164)   HTML8)    PDF (8018KB)(217)      

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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Identification of footwalls and roofs of coal seams in underground coal mines using borehole radar
LIU Si-Xin, SHI Wei, SONG Zi-Hao, CHEN Chun-Lin, DAI Zheng
Geophysical and Geochemical Exploration    2023, 47 (2): 365-371.   DOI: 10.11720/wtyht.2023.1392
Abstract156)   HTML16)    PDF (3287KB)(152)      

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

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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
Abstract152)   HTML7)    PDF (4627KB)(95)      

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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Geochemical characteristics and Cr metallogenic potential evaluation of the middle section of the northern margin of the Qaidam Basin
CHEN Xi, AN Zhao, ZHANG Wen-Quan, XU Yun-Fu, MA Ying, SHI Lian-Chang, TAO Zhi-Hua
Geophysical and Geochemical Exploration    2023, 47 (2): 353-364.   DOI: 10.11720/wtyht.2023.2540
Abstract151)   HTML3)    PDF (8534KB)(160)      

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

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Rapid determination of soil cation exchange capacity using a cation exchange capacity pretreatment system and a Kjeldahl apparatus
HU Meng-Ying, ZHANG Peng-Peng, XU Jin-Li, LIU Bin, ZHANG Ling-Huo, DU Xue-Miao, BAI Jin-Feng
Geophysical and Geochemical Exploration    2023, 47 (2): 458-463.   DOI: 10.11720/wtyht.2023.1133
Abstract149)   HTML2)    PDF (636KB)(118)      

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

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Spatial distribution patterns of concealed plutons in the western Zhen’an area based on gravity anomalies
ZHANG Jin-Ai, YANG Yuan, ZHANG Lin
Geophysical and Geochemical Exploration    2023, 47 (3): 618-627.   DOI: 10.11720/wtyht.2023.1465
Abstract149)   HTML11)    PDF (8220KB)(211)      

The western Zhen'an area enjoys superior ore-forming conditions of tungsten-molybdenum polymetallic deposits. A batch of large and medium-scale tungsten-molybdenum deposits such as Dongyang, Qipangou, Guilingou, Yueheping, and Hetaoping, have been discovered in this area, and they are related to intrusions. To explore tungsten-molybdenum ore bodies, it is necessary to carry out studies on intrusions related to mineralization, especially concealed intrusions. Based on high-precision gravity anomalies, this study extracted the gravity anomaly data of concealed plutons using the minimum curvature potential field separation method. Moreover, it investigated the plane positions of the concealed plutons in the western Zhen'an area by combining the geophysical characteristics of the exposed plutons, identifying five concealed plutons, namely Lanbandeng, Shapingcun, Yuehetai, Dongchuanjie, and Huangjinmei, through investigation. Moreover, this study conducted the 3D gravity anomaly inversion for typical concealed plutons, determining the spatial distribution characteristics of the concealed plutons. The Yuehetai and eastern Lanbandeng concealed plutons have been verified through boreholes, with high-grade wolframite being discovered. The method proposed in this study can provide technical support for the study of concealed plutons in the Zhen'an area and other areas, as well as important data for the study of the tectonic-magmatic-metallogenic evolution of the southern Qinling metallogenic belt.

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The comprehensive evaluation of farmland soil environmental quality and suggestions on the development of agriculture with distinctive local features in Tumed Left Banner, Inner Mongolia
BAO Feng-Qin, CHENG Hang-Xin, YONG Sheng, YANG Yu-Liang, MA Zhi-Chao, ZHAO Li-Juan
Geophysical and Geochemical Exploration    2023, 47 (2): 487-495.   DOI: 10.11720/wtyht.2023.1044
Abstract144)   HTML1)    PDF (3162KB)(163)      

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

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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
Abstract143)   HTML4)    PDF (5856KB)(244)      

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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Application of seismic frequency-divided iterative inversion in the prediction of thinly laminated channel sand bodies
REN Xian-Jun, LI Zhong, MA Ying-Long, DONG Ping, TIAN Xing-Da
Geophysical and Geochemical Exploration    2023, 47 (2): 420-428.   DOI: 10.11720/wtyht.2023.1175
Abstract140)   HTML2)    PDF (6781KB)(157)      

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

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Geochemical characteristics and prospecting potential of Jianchi Town, Shaanxi Province, China based on 1∶25,000 stream sediment survey
ZHANG Jia-Sheng, ZHOU Wei, LI Wei-Liang, QI Xiao-Peng, YANG Jie, WANG Lu
Geophysical and Geochemical Exploration    2023, 47 (3): 659-669.   DOI: 10.11720/wtyht.2023.1122
Abstract136)   HTML215)    PDF (6805KB)(206)      

Jianchi Town of Shaanxi Province is located in the Nanjiang foreland-superimposed basin on the northern margin of the Yangtze Plate. To determine the prospecting potential, this study conducted a 1∶25,000 stream sediment survey in the study area. Based on the testing results of 12 elements and compounds closely related to mineralization, namely K2O, Na2O, CaO, MgO, Cl, S, B, Rb, Cs, Li, Br, and I, this study analyzed the geochemical characteristics of these elements and compounds and determined that Li is the major metallogenic element, Li-B-Rb-Cs-K2O is the indicator element association for the prospecting of lithium deposits, and the spatial morphology of Li agrees with that of various geological bodies. By combining the metallogenic geological setting, this study delineated 18 integrated anomalies. Through the follow-up examination of the anomalies, multiple lithium ore bodies (mineralized points) were discovered, indicating that the study area has favorable metallogenic geological and geochemical conditions and great prospecting potential.

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Speciation of selenium in the selenium-rich cultivated land in Linhe District, Bayannur City, Inner Mongolia and its influencing factors
LI Shi-Bao, YANG Li-Guo, XIONG Wan-Li, MA Zhi-Chao, YUAN Hong-Wei, DUAN Ji-Xue
Geophysical and Geochemical Exploration    2023, 47 (2): 477-486.   DOI: 10.11720/wtyht.2023.1010
Abstract134)   HTML1)    PDF (3596KB)(145)      

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

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Post-stack P-wave impedance inversion based on spectral inversion
XING Wen-Jun, CAO Si-Yuan, CHEN Si-Yuan, SUN Yao-Guang
Geophysical and Geochemical Exploration    2023, 47 (2): 429-437.   DOI: 10.11720/wtyht.2023.1222
Abstract133)   HTML2)    PDF (7004KB)(191)      

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

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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
Abstract133)   HTML9)    PDF (4345KB)(201)      

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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A study of tectonic framework of the Qinnan sag in Bohai Basin and its adjacent areas based on satellite gravity anomalies
YANG Rong-Xiang, WANG Wan-Yin, CAI Meng-Ke, WANG Ding-Ding, LUO Xin-Gang
Geophysical and Geochemical Exploration    2023, 47 (3): 584-596.   DOI: 10.11720/wtyht.2023.1463
Abstract124)   HTML174)    PDF (15824KB)(201)      

The Bohai Basin has the most offshore oil and gas fields discovered in China. As a potential hydrocarbon-rich sag in the Bohai Basin, the Qinnan Sag is of high value in exploration. Therefore, the study of the tectonic framework of the sag and its adjacent areas is of great significance and application value. Based on satellite gravity anomalies, this study determined the Bouguer gravity anomalies by correcting the influences of land topography and seawater and obtained the planar distribution and apparent depths of faults, the thickness of Cenozoic strata, and the boundaries of tectonic units using methods such as the normalized vertical derivative of the total horizontal derivative (NVDR-THDR), the Euler deconvolution, the minimum curvature potential field separation, and the fast for the gravity field based in a dual interface model. Based on the geological and geophysical data, this study analyzed the distribution and geophysical characteristics of major faults and tectonic units in the study area. The results of this study are as follows: The faults in the Qinnan Sag and its adjacent areas mainly have NE, NEE, and NW strikes and an apparent depth of primarily 1~10 km, which is up to 15~25 km at some positions of the sag-controlling faults and the intersections of the faults; The Cenozoic strata have a thickness of 0~11 km. The Cenozoic tectonic units are distributed in alternating NE and NEE directions, and their boundaries are mostly controlled by faults; Through further investigation, this study classified the sub-sag on the west side of the Qinnan sag as the Laoting sag and adjusted the boundaries of other tectonic units. The results of this study on the distribution of the faults and tectonic units can provide geophysical data for hydrocarbon exploration in the Qinnan Sag.

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One-dimensional focusing inversion of the semi-airborne transient electromagnetic method and its application
WANG Shi-Xing, HE Ke, YIN Xiao-Kang, WEI Dong-Hua, ZHAO Si-Wei, GUO Ming
Geophysical and Geochemical Exploration    2023, 47 (2): 410-419.   DOI: 10.11720/wtyht.2023.1337
Abstract121)   HTML2)    PDF (3837KB)(184)      

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

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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
Abstract121)   HTML3)    PDF (4012KB)(109)      

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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Application of the wide-field electromagnetic method in hydrogeological exploration under the extremely-thick low-resistivity layer: A case study of a coal mine in the Huainan area, Anhui Province
Qi Zhao-Hua
Geophysical and Geochemical Exploration    2023, 47 (3): 700-706.   DOI: 10.11720/wtyht.2023.1178
Abstract120)   HTML14)    PDF (4532KB)(208)      

To investigate the water yield properties of the aquifers in the hanging and foot walls of coal seams under the extremely-thick low-resistivity layer, this study conducted the hydrogeological exploration using the wide-field electromagnetic method (WFEM) targeting a coal mine in the Huainan area, Anhui Province. The geological results obtained through multiple means, such as test analysis and data acquisition and interpretation, agree well with the downhole conditions. As indicated by the successful WFEM application in the hydrogeological exploration of the coal mine, the WFEM features strong penetrability, large investigation depth, and high accuracy. Therefore, the WFEM can be used as a new geophysical exploration method for the hydrological survey of large-depth coal fields.

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Geological and geochemical characteristics and prospecting potential of rare element and rare earth element deposits in Saima alkaline complex
NAN Zhe, WANG Lin-Shi, HOU Xu, ZHAI Zheng-Bo, WANG Yang, LIU Yang
Geophysical and Geochemical Exploration    2023, 47 (3): 670-680.   DOI: 10.11720/wtyht.2023.2185
Abstract119)   HTML10)    PDF (5011KB)(180)      

The Saima alkaline complex is a unique and complex geologic body. It is well known for its diverse rock types and mineral types and high contents of uranium, thorium, and rare and rare earth elements. This study analyzed and summarized the geological exploration results of the Saima alkaline complex area in recent years, discovering that the rocks in the second intrusive stage of the Saima alkaline complex show the wide mineralization of rare and rare earth elements, with a moderate- to low- mineralization temperature. There are mainly two types of deposits in Saima alkaline complex area, namely the residual magmatic metasomatism type and the skarn type. Furthermore, the prospecting potential of the whole alkaline complex was analyzed by combining the 1∶200,000 stream sediment survey data and the 1∶10,000 primary halo survey data. Three predicted metallogenic zones of rare earth and radioactive elements were delineated in the Saima alkaline complex and its surrounding area, namely Saima-Gujia, Aiyang, and Shuangshanzi. This study is of great significance for the prospecting of rare and rare earth polymetals in the Saima alkaline complex area.

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Research on structural characteristics and mineral prediction of the Luoning area based on the characteristics of gravitational and magnetic fields
ZHANG Lei, WANG Wan-Yin, WANG Xiao-Bo, LI Wen, ZHANG Xue-Li, SONG Hao, YANG Min, AN Li-ming
Geophysical and Geochemical Exploration    2023, 47 (3): 608-617.   DOI: 10.11720/wtyht.2023.1462
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The Luoning area is located at the junction of the Xiaoshan Uplift and the Luoning Basin and falls into the Quaternary shallow overburden area. Large-scale silver-lead-zinc deposits such as Laoliwan and Zhonghe have been discovered in this area, and their formation is closely related to the acidic plutons controlled by fault structures. This study investigated the distribution of fault structures and acidic plutons based on the processing of 1:50000 gravity and magnetic data using the minimum curvature potential field separation technique, the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) technique, the correlation analysis method, and the three-dimensional physical property inversion. The study results are as follows: (1) The Luoning area is affected by the NW-, NE-, and EW-trending structures; (2) Centering on the Laoliwan area, multiple sets of faults present a ring-shaped distribution with a radius of 6.5 km; (3) Multiple concealed plutons were discovered, and the boundaries of Laoliwan and Zhonghe plutons were re-determined; (4) The distribution of granites is controlled by ring-shaped structures and have a burial depth of about 3 km; (4) The ring-shaped structures are well correlated with magnetic anomaly gradient zones, where ores were found in many boreholes. Therefore, it is of great significance to carry out prospecting studies in these zones.

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Environmental quality characteristics of soil and health risk assessment of crops of farmlands in the southern suburb of Baotou
Bao Feng-Qin, Cheng Hang-Xin, Yong Sheng, Zhou Li-Jun, Yang Yu-Liang
Geophysical and Geochemical Exploration    2023, 47 (3): 816-825.   DOI: 10.11720/wtyht.2023.1159
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To investigate and assess the characteristics of cadmium, lead, and zinc in the soil and crops in the farmland around the old industrial area in the south of Baotou City, this study analyzed and tested the heavy metal content in soil, crop root soil, and seeds, assess the pollution according to relevant standards, and conducted the risk assessment and source analysis of heavy metals using the pollution index, the bioconcentration factor, and human health risk index. The results are as follows:Regarding the soil environmental quality, the soils in the study area are dominated by clean soils, with the polluted soils distributed primarily on both sides of the old sewage canals.The sites of over-limit root soils are also primarily distributed around the old sewage canals.Among the heavy metal morphologies, carbonate-bound, Fe-Mn-bound, and residue heavy metals account for relatively high proportions, while exchangeable heavy metals (water-soluble and ion-exchange) account for relatively low proportions. Most of the seed samples exhibited normal and low enrichment of heavy metals. Compared with other crops, sunflower seeds showed super adsorptivity of cadmium, lead, and zinc, posing significant non-carcinogenic and carcinogenic health risks to children and adults.

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Simulated detection experiments of underground water supply pipeline leakage based on ground penetrating radar
WANG Yu-Cheng, WANG Hong-Hua, SU Peng-Jin, GONG Jun-Bo, XI Yu-He
Geophysical and Geochemical Exploration    2023, 47 (3): 794-803.   DOI: 10.11720/wtyht.2023.1199
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As an important part of urban infrastructure, underground water supply pipelines frequently leak or break due to disrepair,corrosion,and poor construction quality.It is of great significance to identify the leakage locations and affected areas of underground water supply pipelines using a non-destructive testing method for the purpose of early warning and follow-up treatment.This study conducted simulated detection experiments and analysis of underground water supply pipeline leakage using the ground penetrating radar (GPR) method.Firstly,this study established the leakage model of water supply pipelines in sandy soil using the SEEP/W module in the GeoStudio software and calculated the volumetric water content of different leakage locations and leakage times.Then,it established the relative dielectric constant and conductivity model for water supply pipeline leakage using the Topp equation and the empirical equations of electrical conductivity and water content.On this basis,this study conducted the GPR simulated detection of the water supply pipeline leakage model with different leakage locations and different leakage times using the finite difference time domain (FDTD) method and analyzed the simulation results.Finally,this study conducted the GPR-based physical simulated detection tests of water supply pipeline leakage and compared the test results with the numerical simulation results.The study results are as follows.Compared with the hyperbolic diffracted wave of the water supply pipelines without leakage,that of the water supply pipelines with leakage at different locations are stated as follows.For the leakage on the upper side,a longer leakage area and a larger leakage area were associated with an earlier present hyperbolic diffracted wave with weaker energy,while the horizontal position of the hyperbolic diffracted wave's vertex remained unchanged.For the leakage on the lower side,two hyperbolic diffracted waves appeared,which moved up and down individually.Moreover,a longer leakage time corresponded to two weaker and more separated hyperbolic diffracted waves.The horizontal positions of the hyperbolic diffracted waves' vertexes remained unchanged.For the leakage on the left (right) side,a longer leakage time was associated with a weaker hyperbolic diffracted wave,whose vertex deviated farther toward the upper left (right).The simulated detection results of this study can provide a reliable basis for early warning and follow-up treatment of water supply pipeline leakage.

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Application of wide field electromagnetic method in the fracturing monitoring of well Anye-2
HU Zhi-Fang, LUO Wei-Feng, WANG Sheng-Jian, KANG Hai-Xia, ZHOU Hui, ZHANG Yun-Xiao, ZHAN Shao-Quan
Geophysical and Geochemical Exploration    2023, 47 (3): 718-725.   DOI: 10.11720/wtyht.2023.1089
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To evaluate the fracturing performance of two horizontal wells of well Anye-2,this study explored the layout of the fracturing monitoring network and data acquisition and processing using the fracturing monitoring technique combined with the wide field electromagnetic method.Through the qualitative and semi-quantitative difference analysis of the pre-,in-,and post-fracturing monitoring data,this study preliminarily determined the propagation direction of induced fractures and semi-quantitatively calculated the parameters such as fracture length and height.For each fracturing interval,the parameters such as fracture height and length were quantitatively determined through fine-scale inversion with depth as constraints and difference calculation.The fracturing monitoring results show that the fractures at two horizontal wells had lengths of 100~125 m and heights of 20~25 m.The fracturing production was guided by evaluating the fracturing performance of each fracturing interval.The fracturing results of the previous interval were used to guide the fracturing of the subsequent interval.Finally,the fracturing performance of all fracturing intervals was evaluated.The application results show that the wide field electromagnetic method can effectively predict the spread direction and range(e.g.,fracture length) of fracturing fluids,achieving encouraging performance.

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Application of the DC resistivity method in the study of saline groundwater distribution in the lower reaches of the Yellow River
XU Yan, ZHANG Tai-Ping, XIE Wei, ZHANG Hong-Jun, WANG Qiang, WANG Wei, GUO Peng, WANG Kui-Feng, YIN Ji-Guang, ZHANG Rui-Hua
Geophysical and Geochemical Exploration    2023, 47 (2): 496-503.   DOI: 10.11720/wtyht.2023.1034
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This study investigated the distribution characteristics of saline groundwater in the Huimin area of the lower reaches of the Yellow River using the DC resistivity method. Specifically, this study determined the distribution range of the apparent resistivity of the saline water and the variation in the saline-fresh groundwater interface in the area based on resistivity logs, aiming to constrain the resistivity sounding data analysis and improve the interpretation accuracy of the distribution of the saline groundwater. The results are as follows. The top boundary of the saline water in the area mainly had a burial depth of 20~50 m and developed to the shallow surface locally. It was inferred that the bottom boundary of the saline water had a burial of mainly 160~300 m and gradually became shallow in a nearly NW direction. As verified by the later investigation of water samples and drilling, the inferred saline groundwater characteristics agreed roughly with the actual situation. This result indicates that the DC resistivity method has a good application performance in the study of the distribution of saline groundwater.

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Application of the geochemical block method to the assessment of copper resources in Ethiopia
XIANG Wen-Shuai, BAI Yang, JIANG Jun-Sheng, LEI Yi-Jun, HUNDIE Melka, SISAY Degu, ZHANG Yuan-Pei, WU Ying, ZHENG Xiong-Wei
Geophysical and Geochemical Exploration    2023, 47 (4): 845-855.   DOI: 10.11720/wtyht.2023.1198
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Low-density geochemical mapping is characterized by high order streams to be sampled and a large coverage area and can be used to effectively trace geochemical blocks with high metal contents. Based on the 1:1,000,000 low-density geochemical mapping data of Ethiopia and the processing of the testing data of Cu in the original stream sediments, this study calculated the anomaly threshold of Cu at 37×10-6 through iterative deletion. Then, this study delineated three geochemical blocks and two regional anomalies with 37×10-6, 42×10-6, 47×10-6, 52×10-6, 59×10-6, and 66×10-6 as grading intervals. It calculated the mineralization coefficient of Cu ore bodies in the study area at 0.055% by referencing the known reserves of Cu deposits in geochemical blocks with a high level of copper exploration in the same metallogenic belt. Moreover, this study estimated the Cu resources in the study area at 2,600,000 t based on a rock mass thickness of 1,000 m. By combining the analysis of metallogenic geological conditions, this study determined that the zones where geochemical blocks nos. 2, 3, and 4 are located can be considered key metallogenic prospect areas for further detailed exploration.

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Influence of DEM grid spacing and correction radius on terrain correction in gravity exploration
ZHANG Fei-Fei, WANG Wan-Yin, LI Qian, WANG Lin, MA Jing
Geophysical and Geochemical Exploration    2023, 47 (3): 597-607.   DOI: 10.11720/wtyht.2023.1472
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To remove the effect of terrain mass on observed gravity values, it is necessary to conduct terrain correction in gravity exploration. Terrains have the greatest impact on gravity values because they are the closest to observation points. However, the complex topographic relief makes it difficult to precisely determine the variation of topographic relief. Therefore, terrain correction is the most critical factor in the improvement of the precision of gravity exploration. The grid size of terrain data and the terrain correction radius are the key factors affecting the calculation precision of terrain correction. This study collected the DEM data with resolutions of 5 m, 10 m, 25 m, 50 m, and 100 m for plains, hills, and mountains. Based on these data, this study calculated conventional and generalized terrain correction values under different grid spacings and correction ranges and analyzed the influence of different grid spacings and correction radii on terrain correction in gravity exploration. The results are as follows: the gravity effect of the terrain mass above the geoid on the observation points was mainly concentrated in the range of 0~5 000 m and accounted for about 90% of the influence value of the total terrain mass. Attention should be paid to the correction of the middle and far areas during the terrain correction of hills and mountains, and it is necessary to appropriately increase the correction range of the middle areas; Different types of terrains had different requirements for grid spacings, and greater variations in topographic relief imposed higher requirements for the resolution DEM data. Based on the results of the comparative analysis, this study proposed some suggestions on the selection of DEM grid spacings and correction radii for different types of terrains. This study provides an important reference for the theoretical study and specification refinement of gravity terrain correction and has a great prospect for applications.

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Migration and enrichment patterns of vanadium in the soil and plant system of farmland
ZHAO Yu-Yan, JIANG Tao, YANG Bing-Han, ZHANG Ze-Yu, LI Zheng-He, LI Bing, TANG Xiao-Dan
Geophysical and Geochemical Exploration    2023, 47 (3): 835-844.   DOI: 10.11720/wtyht.2023.1206
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Vanadium (V) is an essential trace element required by organisms for maintaining their normal life activities. It is also a harmful element listed as a priority environmental pollutant by the United Nations Environment Programme (UNEP). The study of the migration and enrichment patterns of V in the soil and plant system is of great practical significance for further understanding the ecological geochemical behavior of V and ensuring the safety of agricultural products and human health. This study systematically sampled the soil and plants in some ordinary farmland in Linyi City, Shandong Province and analyzed and tested the contents of V and its associated elements in the soil and plant samples. Moreover, this study conducted the source analysis and pollution assessment of V and investigated the migration and transformation patterns of V in the soil-plant system using statistical methods such as descriptive statistics, correlation analysis, and cluster analysis, as well as the single factor pollution index method, the potential ecological risk index method, and the biological enrichment coefficient method. The results are as follows: V is relatively concentrated in the study area, and its content increases with an increase in the Fe and Ti contents and decreases with an increase in the SiO2, Na2O, Sr, and CaO contents; The V in the study area mainly originates from the weathering of parent rocks, and the parts with a high V content is related to magnetite; As shown by the results of the single factor index method and the potential ecological risk index method, V is relatively clean in the soils of the study area, but attention should be paid to the pollution of the associated Cd; V is enriched primarily in the roots of plants, and plants' absorption capacity of V is generally negatively correlated with the contents of Cu, Pb, Zn, Ni, Co, Cd, and especially Cr in soils and is positively correlated with the As content in soils. This study enriches the ecological geochemical theory of V and provides a scientific basis for regional agricultural production, environmental quality assessment, and ecological pollution control.

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Regularized joint inversion of magnetotelluric and gravity data based on inequality and Gramian constraints
CHEN Xiao, ZENG Zhi-Wen, DENG Ju-Zhi, ZHANG Zhi-Yong, CHEN Hui, YU Hui, WANG Yan-Guo
Geophysical and Geochemical Exploration    2023, 47 (3): 575-583.   DOI: 10.11720/wtyht.2023.1474
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Regularized joint inversion based on Gramian constraints is a hot research topic in the field of geophysical joint inversion. Given the difficulty in selecting weighted factors of the regularization and constraint items, it is necessary to introduce inequality constraints into the regularized joint inversion. To investigate the regularized joint inversion of magnetotelluric (MT) and gravity data based on Gramian constraints, this study compared the application effects of the penalty function method and the transform function method in the joint inversion and processed the measured data of a survey line in Xiangshan, Jiangxi Province. According to the results from model experiments, both methods can effectively constrain petrophysical parameters, and the penalty function method has higher flexibility but requires the artificial setting of the weighted factors. Moreover, the processing of the measured data shows that the joint inversion based on inequality and Gramian constraints is highly practical and can improve the precision of geophysical interpretation.

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Formation mechanisms and significance of saline-lacustrine Se-rich soils in the Xining Basin
ZHANG Ya-Feng, JI Bing-Yan, SHEN Xiao, YAO Zhen, MA Qiang, WANG Shuai, HE Lian-Zhen, HAN Wei-Ming
Geophysical and Geochemical Exploration    2023, 47 (2): 470-476.   DOI: 10.11720/wtyht.2023.1325
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As shown by the investigation and analysis of the Se content in soils and rocks of the Xining Basin, the rocks and soils in the Paleogene Xining Formation and the Cretaceous Minhe Formation have the highest Se content, which makes them the major Se-rich parent materials of soils in the basin. By combining the paleogeographic data on the retreating process of the basin, it can be concluded that the Paleogene Xining Formation and the Neogene Guide Group were deposited from the arid and hot saline lacustrine facies to the humid and cool saline-freshwater lacustrine facies. The combined action of the saline lake boundary and the arid and hot saline-lacustrine environment, as well as the following transformation by landforms and water systems, contributed to the formation of the existing framework of saline-lacustrine sedimentary Se-rich soils in the Xining Basin. Such Se-rich soils enjoy the advantages of a low heavy metal content, a moderate Se content, and a high available Se content and thus are of great value in development and utilization.

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Frequency-domain 2D seismic forward modeling method based on the LSCG method and the wavenumber compensation
ZHANG Ru-Hua, ZHANG Dong-Jun, HUANG Jian-Ping, GOU Qi-Yong, ZHOU Jia-Ni
Geophysical and Geochemical Exploration    2023, 47 (2): 384-390.   DOI: 10.11720/wtyht.2023.2633
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The seismic forward modeling technique is critical to seismic exploration.Moreover,it shows a faster rate and higher calculation efficiency in the frequency domain than in the time domain.Presently,there is a need to complete the forward calculation in the frequency domain efficiently and accurately.The specific problems include the numerical dispersion and the high memory consumption for calculating and decomposing impedance,which should be reduced by improving the calculation efficiency.Different from the conventional direct method,this study adopted the least-squares conjugate gradient (LSCG) method used to determine the impedance matrix for the frequency-domain forward modeling and proposed an expression for wavenumber compensation to suppress the numerical dispersion.The numerical tests of simple and complex models show that the LSCG method can effectively reduce the calculation time and that the frequency-domain forward modeling method based on wavenumber compensation can effectively suppress the numerical dispersion and thus improve the precision of wave field simulation.

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Migration of heavy metals in the soil-tea plant system and health risks of drinking tea: A case study of Qiongzhong County, Hainan Province
GONG Qiu-Li, YANG Jian-Zhou, WANG Zhen-Liang, YAN Hui
Geophysical and Geochemical Exploration    2023, 47 (3): 826-834.   DOI: 10.11720/wtyht.2023.1321
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This study sampled the soil and the corresponding roots, stems, and leaves (including large leaves, new leaves, and sprouts) of tea plants from three ecological tea plantations in Qiongzhong County, Hainan Province. Based on these samples, this study investigated the migration of heavy metals in the soil-tea plant system and analyzed the migration patterns of heavy metals and the health risks caused by heavy metals in tea. As indicated by the results, the Pb, Cr, Cd, As, and Hg concentrations in the soil are slightly higher than the background values of corresponding soil elements in Hainan, showing non-significant accumulation. The enrichment of heavy metals varies significantly in different organs of tea plants. Specifically, Cr, Zn, Pb, Hg, and Cd are enriched in roots, while Cu and Ni are enriched in leaves; Pb, Cd, and Hg have higher concentrations in large leaves than in new leaves and sprouts, indicating that these elements are enriched with the growth of leaves; Cu, Ni, and Zn have higher concentrations in sprouts than in leaves, showing that these elements are enriched in the growing parts of leaves. Bio-concentration factors (BCF) indicate that soil physicochemical composition, heavy metal species, and leaf age have effects on the absorption of heavy metals by tea leaves. The results of the risk assessment show that the target hazard quotients (HQ) and hazard indices (HI) of all samples are less than 1, indicating acceptable health risks caused by heavy metals in tea. This study can provide a scientific basis for the prevention and control of heavy metals in tea plantations and has a positive guiding significance for managing tea plantations and ensuring the health of tea consumers.

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Airborne Bouguer gravity based on synchronous terrains surveyed using helicopter airborne gravimetry
QU Jin-Hong, JIANG Zuo-Xi, ZHOU Xi-Hua, WANG Ming, LUO Feng
Geophysical and Geochemical Exploration    2023, 47 (2): 447-457.   DOI: 10.11720/wtyht.2023.1289
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Large-scale mining activities have been continued in key exploration areas. Consequently, the mined-out areas, waste dumps, and tailings ponds of mines are constantly deforming. As a result, the digital terrain method fails to make the terrain data closely match the airborne gravimetric data, leading to serious correction errors in airborne gravity terrain correction and stone-slab correction. This study calculated the difference between the GNSS geodetic height and the radio terrain clearance altitude of the helicopter gravity and magnetic survey system and then converted the GNSS geodetic height into normal height. Then, the synchronous surveyed terrains were obtained through leveling and fine-scale processing. Moreover, the surveyed terrain data, together with various collected terrain data, were compared with the ICESat-2/ATL08 spaceborne laser elevation. The results show that the surveyed terrains Wxd100 and Wxd400 had elevation precision of 5.33 m and 8.93 m, respectively. After airborne Bouguer gravity correction was conducted using the surveyed terrains, the data quality of the mining area and several typical survey lines was greatly improved.

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