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  • Table of Content
      20 August 2019, Volume 43 Issue 4 Previous Issue    Next Issue
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    Applied geochemistry for future resource exploration —Summary of the 28 th IAGS conference
    Ming-Qi WANG, Rong YE
    Geophysical and Geochemical Exploration. 2019, 43 (4): 679-691.   DOI: 10.11720/wtyht.2019.0291
    Abstract   HTML ( 421 )   PDF (616KB) ( 820 )

    As partner of the Resources for Future Generations 2018 Conference, the Association of Applied Geochemists (AAG) holded the IAGS 2018 symposium as an integral component of the RFG18 conference in Vancouver, BC, Canada during June 16~22, 2018. The RFG covered Energy, Minerals, Water and the Earth. 113 oral presentations showcasing through specific the advancements and applications of geochemistry in the spheres of exploration and environment were made in 10 AAG sessions covering Minerals and Water during the IAGS 2018 symposium.

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    A geochemical ore-prospecting experiment by extracting Fe-Mn oxides bound in soil samples in the Toudaojing Cu-Au deposit in Xin Barag Right Banner, Inner Mongolia
    Fan YANG, Zhi-Hong HAO, Su-Rong ZHANG, Jin-Li XU, Jing-Bin WANG, Hang-Xin CHENG, Rui-Zhong HU, Shun-Yao ZHANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 692-701.   DOI: 10.11720/wtyht.2019.0013
    Abstract   HTML ( 13 )   PDF (4857KB) ( 644 )

    The ore-prospecting effect of the stream sediment survey and the soil geochemistry survey is not ideal in the covered areas of the hilly grassland landscape where the water system is not developed whereas the aeolian sand is very developed. Therefore, it is imperative to carry out some new ore-prospecting experiment for prospecting breakthrough. In this study, the experiment was carried out by using the Fe-Mn oxides bound in the soil samples in a selected experimental site. The Toudaojing Cu-Au deposit in Xin Barag Right Banner of Inner Mongolia was selected as the experimental site. Soil samples were collected in the ore area and its periphery. Element concentrations in the Fe-Mn oxides bound in soil samples were determined by matched analysis of scheme including plasma mass spectrometry, atomic fluorescence spectroscopy and flameless atomic absorption spectrometry. Areal test for this geochemical ore-prospecting technique was carried out for delineating geochemical anomaly. Geochemical anomaly was verified by drilling, and new concealed gold orebodies were found. The results show that accuracy and precision tests of the analytical method could satisfy the requirements of geochemical ore-prospecting. The Fe-Mn oxides bound in soil samples can effectively delineate the prospecting target area and find concealed gold deposits in the Toudaojing Cu-Au deposit in Xin Barag Right Banner of Inner Mongolia. Therefore, it is a successful case of geochemical ore-prospecting in the covered area.

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    Characteristics of rock geochemical anomalies and prospecting potential of the Sinongduo silver polymetallic deposit, Tibet
    Zong-Yao YANG, Chong-Hai ZHANG, Xiao-Yan ZHAO, Xing-Hai LANG, Hong-Tian XIAO, Jun LIANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 702-708.   DOI: 10.11720/wtyht.2019.2457
    Abstract   HTML ( 7 )   PDF (4541KB) ( 664 )

    The Sinongduo silver polymetallic deposit is the first low sulfidation epithermal deposit found in the Linzizong volcanic rocks. Its unique origin and metallogenic geological background indicate great prospecting potential of the south Gangdise metallogenic belt. The zoning characteristics of metallogenic elements were studied by means of large scale rock geochemical survey in the Sinongduo deposit. The large coefficient of variation and standard deviation of Pb, Zn, Cd, Ag and Au indicate the high enrichment and enrichment capability of these elements. Cluster analysis shows high correlation between Pb, Zn, Cd, Ag and Au which are considered to be the main mineralization elements. Element anomalies are classified according to the cumulative frequency of 75%, 95% and 98.5% and 2 anomalies area are considered to have high prospecting potential. The authors are in the hope that the data obtained can provide a guide for the geochemical prospecting in the Gangdise metallogenic belt.

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    Exploration in coverage area: A case study of the Changtuxili Mn-Ag-Pb-Zn polymetallic ore deposit,Inner Mongolia
    Yi-Xing MA, Ting-Jie YAN, Peng HE, Zu-Jian LIU, Hang SU, Shuo GUO
    Geophysical and Geochemical Exploration. 2019, 43 (4): 709-717.   DOI: 10.11720/wtyht.2019.1432
    Abstract   HTML ( 13 )   PDF (4449KB) ( 846 )

    The Changtuxili Mn-Ag-Pb-Zn polymetallic ore deposit in Inner Mongolia was first discovered by 1∶50 000 soil geochemical survey; nevertheless, the area is covered with thick overburden and the recognition of surface outcrop is difficult. In order to further determine the favorable position for prospecting, the authors, based on the 1∶50 000 soil survey results, delineated seven IP anomalies by 1∶10 000 IP mid-elevator survey and bathymetry, and analyzed the scale and spatial location of buried polarizable body in sounding profile, thus effectively reducing the range of prospecting target area. Some sounding profiles were drilled to verify the discovery of multi-layered orebodies, which confirms the effectiveness of induced polarization method in prospecting in the study area. In addition, Jd6 is the largest IP anomaly found in the area, which can serve as a key target area for further prospecting. Based on summarizing the exploration work, the result provides a reference for prospecting in this kind of covered areas.

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    The application of magnetotelluric sounding to geothermal resources assessment in Yinchuan Basin
    Huai-Liang ZHU, Bo-Wen XU, Zhi-Long LIU, Feng SHI, Yu-Qi XIN, Xue-Gang CAO, Guo-Qiang Cheng
    Geophysical and Geochemical Exploration. 2019, 43 (4): 718-725.   DOI: 10.11720/wtyht.2019.1361
    Abstract   HTML ( 13 )   PDF (4567KB) ( 994 )

    As a kind of clean and continuous energy, geothermal resources will play an enormous role in the development of China’s economy. In this study, data processing and analysis included calculation of 2D skewness and electric strike of the MT profile, and NLCG 2D inversion was performed on TM data, which consisted of 51 measurement points from line L1 and line L2 in western area of Yinchuan Basin. The result shows that the western margin of the Yinchuan Basin can be divided into three layers from top to bottom:low-resistivity layer, relatively high-resistivity layer and low-resistivity layer. Combined with the known geothermal geological data, the authors hold that Hongliugou Formation of Neogene is the principal heat reservoir and exploitation bed, followed by Qingshuiying Formation of Palaeogene and Ganhegou Formation of Neogene. The result shows that using MT method can well delineate the range of deep geothermal reservoir in the Yinchuan Basin and that MT method is suitable for exploring buried geothermal resources in deep plain.

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    Application study of radon gas and CSAMT joint detection in the uranium exploration in the Wushijiazi Basin of Inner Mongolia
    Yan-Qing WU, Shi-Chen WANG, Yuan DIN, Qing WANG, Wen-Zheng WANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 726-733.   DOI: 10.11720/wtyht.2019.0018
    Abstract   HTML ( 6 )   PDF (1340KB) ( 467 )

    The uranium mineralization in the Wushijiazi volcanic basin enjoys a superior geological conditions. The uranium mineralization anomalies have been found on the surface, and they are of altered and fractured zone type. To identify the extension changes of ore-controlling fracture along the strike and dip as well as the favorable enrichment of uranium orebody, the authors carried out deep exploration. The joint detection of radon gas and CSAMT (Controlled Source Audiofrequency Magnetotelluric) was adopted in the study area where uranium mineralization is densely concentrated. The major structure and characteristics of ore-controlling fracture were identified, and six uranium mineralization favorable places were predicted, among which two places were drilled to verify, and industrial uranium orebodies were found in these two places. It is shown that the joint detection of radon gas and CSAMT is significantly effective in the search for concealed faults and fractures and blind orebodies; it can be adopted in the prospecting work of the uranium deposit with a major ore-controlling factor of fault structure, and can provide the future uranium deposit prospecting work with some ideas and directions, so as to accelerate uranium deposit prospecting work.

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    The geophysical field characteristics of geothermal field with banded reservoir: Taking an example of Reshui-Town geothermal field, Hunan Province
    Bao-Feng ZHAO, Qi-Nian WANG, Da-Wei GUAN
    Geophysical and Geochemical Exploration. 2019, 43 (4): 734-740.   DOI: 10.11720/wtyht.2019.1443
    Abstract   HTML ( 8 )   PDF (3263KB) ( 668 )

    The Reshui-Town geothermal field in Hunan Province is one of the highest temperature and largest reserves geothermal field in the southeastern coastal area, and the reservoir form is banded. In order to analyze the distribution law of the reservoir and guide the exploration in similar areas, high-precision gravity and magnetic measurement and controlled source audio magnetotelluric measurement (CSAMT) were arranged in the area to construct the fault system and analyze the geophysical field characteristics of an excellent thermal reservoir zone. The results as following: 1. Two groups of four-direction faults were developed in the area. The first group was the early vertical NNE and NWW faults, and the second group was the late formation angle of about 75° near NS and NEE. 2. The excellent thermal reservoir is located near the intersection of NWW fault F4 and near NS fault F7. It shows the boundary of gravity between the low value area and the high value area, the boundary of low magnetic anomaly and high anomaly, electricity Vertical electrical low resistance zone on the cross section of the method.

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    A study of chemical characteristics and water-rock interaction of karstic geothermal reservoir in Wuhan city circle
    Jun-Qiang NIU, Wei FAN, Kun GUO
    Geophysical and Geochemical Exploration. 2019, 43 (4): 741-748.   DOI: 10.11720/wtyht.2019.1400
    Abstract   HTML ( 3 )   PDF (1442KB) ( 597 )

    Based on the geothermal water hydrochemical data of karst geothermal fields of Wuhan urban agglomeration, the authors summarized the hydrochemical type of karst hot mineral water, analyzed the variation characteristics of main components of karst hot mineral water with temperature, studied the relationship between the degree and time of water-rock action, and analyzed the hydrochemical processes of the main ions in hot water. The results show that the content of main components in hot water is controlled by temperature and water-rock interaction process, the total dissolved solids content increases with the increase of water-rock action time. As the total dissolved solids content increases, the water-rock interaction was gradually transformed from carbonate dissolution to sulfate dissolution, at high total dissolved solids, the dissolution of salt rocks is enhanced. the Langkou geothermal field, the Wuhongshan geothermal field and the Shewushan geothermal field belong to the same water flow system, the Tangchi geothermal field and the Makou geothermal well belong to the same water flow system, and other geothermal fields belong to separated water flow systems.

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    Thermomagnetic component measurement: A geochemical prospecting method for transported overburden region
    Shi-Xin TANG, Jian-Jun LI, Sheng-Ming MA, Shu-Qi HU
    Geophysical and Geochemical Exploration. 2019, 43 (4): 749-757.   DOI: 10.11720/wtyht.2019.0041
    Abstract   HTML ( 188 )   PDF (4942KB) ( 669 )

    Aimed at the technical problem of ore-prospecting in transported overburden region, the authors carried out experimental studies of the method of thermalmagnetic component measurement in the known mining areas, which included the Caijiaying hydrothermal type lead-zinc-silver deposit in Hebei Province, the Shaquanzi magmatic copper-nickel sulfide deposit in east Tianshan, and the skarn type iron-copper polymetallic deposit in Yemaquan area. The experimental results of Caijiaying and Shaquanzi area show that, compared with the small and weak anomalies obtained by conventional soil measurement, the surface anomalies measured by thermal-magnetic components are significant, which can well reflect the spatial location and distribution pattern of deep orebodies and have the advantages of strengthening weak anomalies and discovering new ones. The results of the experiment in Yemaquan area show that there are anomalies delineated by thermomagnetic component measurement at the known mining areas with transported sediments covering more than 100 meters. And well matched abnormal elements in space provide a new target area for prospecting in the unknown area. It has been proved by experiments that the thermomagnetic component measurement technology provides an effective method for solving the problem of ore-prospecting in the transported covered region.

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    Two-dimensional seismic and ore-level geological characteristics of Liyuan salt deposit in Puyang County,Henan Province
    Wan-Zhong LI, Chong-Yang CHAI, Ke-Ying LI, Wei SONG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 758-766.   DOI: 10.11720/wtyht.2019.1439
    Abstract   HTML ( 3 )   PDF (8594KB) ( 591 )

    The Liyuan rock salt mining area in Puyang County of Henan Province is located in the Qianliyuan deposition center of the tectonic unit of the Dongpu sag.Based on the exploration of regional mineral resources,the authors carried out a general survey of the rock salt resources in this area.Through the "two-dimensional earthquake first,borehole verification,digital logging,indoor laboratory" and other means,the distribution characteristics,depth and thickness of sand-salt in this area were basically ascertained.The rock salt deposits in the area have continuous multi-phase,strong amplitude,high apparent resistivity and low natural gamma.The vertical direction is the rhythmic layer change of salt rock-gypsum salt rock-mudstone.The exploration results of rock salt resources reaching a very large scale indicate the feasibility of two-dimensional seismic exploration in rock salt exploration.The high data-to-noise ratio raw data and fine interpretation of the data constitute the basis for obtaining rich geological results.

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    Characteristics of gravity and magnetic fields in Ordos Basin and their geological significance
    Bing LI, Yan-Bing SONG, Lei SHI, Qi WANG, Jiu-Ming JIANG, Jiu-Qiang JIN, De-Wen ZHOU, Ming XU, Gang-Yi XIAO, Min-Ying XIE
    Geophysical and Geochemical Exploration. 2019, 43 (4): 767-777.   DOI: 10.11720/wtyht.2019.1391
    Abstract   HTML ( 3 )   PDF (3147KB) ( 2270 )

    According to aeromagnetic and gravitational data, the boundary and range of Ordos basin were determined based on an analysis of the characteristics of gravity and magnetic fields. And on the basis of compiling depth map of the metamorphic basement and structuring zoning map, research was conducted on the basin’s basement structure, characteristics and features of depth change, structure framework, and caprock thickness. The research indicates that the metamorphic basement is composed of Proterozoic metamorphic series, and the buried depth of crystalline basement can reach 5 000 to 20 000 meters. The caprock is the layers of Ediacaran, Paleozoic, and Mesozoic. The occurrence and development of the basin are restricted by nearly NE-and NWW-trending structures, forming a pattern of four depressions and three uplifts. All the new understanding and conclusions provide a reference for further oil and gas exploration in the basin.

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    The petrophysical characteristics of Upper Paleozoic source rocks from the central and southern part of the Da Hinggan Mountains
    Yong-Zhen YUAN, Peng-Hui ZHANG, Xiao-Bo ZHANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 778-782.   DOI: 10.11720/wtyht.2019.0087
    Abstract   HTML ( 4 )   PDF (897KB) ( 530 )

    Based on a study of regional stratigraphic development characteristics, the authors hold that the Upper Paleozoic in the central and southern part of the Da Hinggan Mountains has a good prospect for oil and gas exploration. In this study, stratigraphic physical specimens were systematically collected from Jarud basin, Tuquan basin and Ulanhot area, and density, magnetization and resistivity were analyzed. Combined with the previous character research data and the results of this work, the petrophysical parameters of the strata in Jarud basin, Tuquan basin and Ulanhot area were systematically sorted out, and the petrophysical interface of the strata in Linxi formation of the Upper Paleozoic was emphatically analyzed, thus providing basic data for the non-seismic geophysical survey in this area. A comparative study of two aspects of paleogeographic environment and physical characteristics shows that the hydrocarbon source rock strata of Linxi Formation in three areas are different. It is considered that the conditions for the formation of hydrocarbon source rock in Tuquan basin area are relatively favorable and, in addition, the degree of slatinization of mudstone is low, suggesting that this area is the most favorable area in the search for hydrocarbon source rock of Linxi Formation.

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    The application of direct-current sounding method in the coastal plains: A case study of Guanyun area in Lianyungang
    Shao-Bing TIAN, Xiang-Qian LI, Tong-Xiao SHANG, Jian OU, Da-Lian ZHANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 783-793.   DOI: 10.11720/wtyht.2019.0054
    Abstract   HTML ( 200 )   PDF (14412KB) ( 824 )

    In this study, the authors used direct-current sounding method (DC method) to explore the electrical resistivity property of Guanyun area in northern Jiangsu basin, based on the 1:50000 geological map. In combination with drilling, well-logging, geological combined profile and shallow layer reflection methods, the authors evaluated the economics and effectiveness of the DC method. The authors obtained the geomorphological electric characteristics of the study area based on the DC method,which provided a basis for the desalinization of saline-alkali land in the study area. The authors first obtained the distribution of brackish water in this area based on the salinization characteristics of underground water, and provided a guidance for the use of fresh water resources. Then, the authors described the distribution of fractures and regional bedrock surface, and fixed the location of the Huaiyin-Xiangshui fault in the northeastern part of the study area. In combination with the results of drilling, the authors holds that DC sounding is an effective and simple method of geological mapping in plain area and will be a useful compensation of the low borehole density in the study area. Therefore, it is suggested that the DC method is an effective exploration method and can be widely used in geological mapping in plain areas.

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    Two-dimensional anomaly characteristics of the magnetotelluric method for a symmetrical anisotropic body
    Miao-Xin YANG, Han-Dong TAN, Sheng-Jun LIANG, Xin WANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 794-803.   DOI: 10.11720/wtyht.2019.1266
    Abstract   HTML ( 6 )   PDF (4576KB) ( 615 )

    Lots of observational data have indicated that anisotropic physical properties are common in rocks in the depth. This requires the construction of anisotropic models to obtain a true reflection of the underground medium. The basis of the present study is a review of previous research results and an investigation of the electrical properties of a layered medium representing actual geological conditions. For a symmetrical anisotropic body, an anisotropy coefficient is proposed, together with an equation for the variation of the Earth's electromagnetic field regarded as two-dimensional. Finally, a finite element simulation of a symmetrical anisotropic body is described. The finite element calculation results are compared with finite difference results to verify the accuracy of the FE program. Three sets of model conditions are considered: (1) fixed anisotropy coefficient and different dip angles, showing the effect of dip angle on an anisotropic body; (2) fixed dip angle and different anisotropy coefficients, showing the effect of the anisotropy coefficient on an anisotropic body; (3) different dip angles and different anisotropy coefficients. Forward pseudo section maps clearly demonstrate the relationship between dip angle, anisotropy coefficient and their anisotropic effect.

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    Time-lapse characteristics analysis of hidden dangers of three-dimensional finite element levees based on unstructured grids
    Da-Li SUN, Xiu LI, Yan-Fu QI, Nai-Quan SUN, Wen-Zhong LI, Jian-Mei ZHOU, Wei-Min SUN
    Geophysical and Geochemical Exploration. 2019, 43 (4): 804-814.   DOI: 10.11720/wtyht.2019.0045
    Abstract   HTML ( 5 )   PDF (9599KB) ( 593 )

    The internal hidden danger of earth-rock dams is the main cause of dyke accidents, which seriously threatens the safety and stability of the dam. Since the hidden danger of the dam will change with the shape and size over time, it shows obvious electrical structural changes. Therefore, the real-time monitoring of the earth dam can be realized by the time-lapsing resistivity imaging method, so as to achieve the purpose of rapid warning of hidden dangers of the dam and avoid them in time. The damage is caused by hidden dangers. However, the current time-lapsing electric dam hidden danger monitoring technology is mainly based on one-dimensional or two-dimensional medium model, which cannot accurately describe the time-lapse electrical characteristics of three-dimensional dam structure. For this reason, based on high-density DC resistivity detection theory, the authors used the three-dimensional non-structural finite element numerical simulation forward modeling method to simulate the time-lapse variation characteristics of the DC electric field in a typical dam hidden danger model and analyzed the response change law. The results of time-shift monitoring have a good reflection of the trend of hidden dangers of dams. The changes in the size, location and shape of dams can cause regular changes in the amplitude and location of the monitoring. The research results of this paper can provide theoretical guidance for the anomaly identification and disaster warning of time-lapse monitoring of dams.

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    A study of automatic correction method for the influence of formation water salinity on compensating neutron logging
    Peng-Ju LI, Yong-Yong LI, Mao-He XU, Yong-Lu FU, Tian TIAN
    Geophysical and Geochemical Exploration. 2019, 43 (4): 815-821.   DOI: 10.11720/wtyht.2019.0012
    Abstract   HTML ( 197 )   PDF (2820KB) ( 679 )

    In the previous Monte Carlo numerical simulation of compensated neutron logging, formation water salinity was mostly set at 0, but in fact, the alteration of formation water salinity would affect compensated neutron logging. In this paper, Monte Carlo method was used to simulate the influence of formation water salinity on compensated neutron logging, and its correction method was proposed. The relationship between salinity and counting rate, salinity and counting ratio, and the effect of salinity on the relationship between counting ratio and porosity and porosity sensitivity under different porosity conditions were simulated successively. According to the calculated results, under the same porosity condition, the counting rate decreases with the increase of salinity, and the counting rate of far detector decreases faster than that of near detector; the near-far counting ratio increases linearly with the increase of salinity as a quadratic function; based on a large number of simulation data, a bivariate function relationship between porosity and salinity is established for different formation water salinity conditions, which eliminates the influence of formation water salinity on compensated neutron logging. In addition, the sensitivity of porosity is obviously affected by salinity in medium and low porosity formations. The bivariate function relation between porosity and salinity established in this paper has completed the automatic correction of salinity effect, simplified the subsequent correction work related to formation water salinity effect, avoided complex instrument re-calibration, and provided a theoretical basis for accurate evaluation of reservoir porosity.

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    The determination of trace tin in water samples by inductively coupled plasma mass spectrometry (ICP-MS) after separation and enrichment using mercapto containing dextran gel
    Bing-Xu XU, Xia XING, Jin-Li XU, Hai-Jie CHEN, Qin ZHANG, Ya-Xuan LIU
    Geophysical and Geochemical Exploration. 2019, 43 (4): 822-827.   DOI: 10.11720/wtyht.2019.1460
    Abstract   HTML ( 2 )   PDF (986KB) ( 634 )

    The content of tin in geochemical water samples is generally low, and there is no standard method which can be used currently. In this investigation, the trace tin in water samples was detected by inductively coupled plasma mass spectrometry (ICP-MS) after separation and enrichment using mercapto containing dextran gel (SDG). The separation conditions of the SDG column were optimized. The separating effect of tin was the best when the acidity of the solution before filtering by the column was 1% (v/v) hydrochloric acid, the ion strength was 0.1mol/L counted by NaAc, the acidity of eluent was 6N hydrochloric acid and the volume of the eluent was 30 mL. When the proposed method was applied to analyzing actual water samples, the detection limit of tin was 0.37μg/L, the precision (RSD%) was less than 10%, and the recovery rate was in the range of 90%~110%, which could satisfy the determination requirement of trace tin in geochemical water samples.

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    The processing technology of narrow azimuth Quasi three-dimensional seismic data acquisition by single source and single long streamer system in marine seismic exploration
    Gui-Lin DENG, Long-Xiang DING, Fu-Yuan LI, Bao-Jin ZHANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 828-834.   DOI: 10.11720/wtyht.2019.1194
    Abstract   HTML ( 206 )   PDF (6612KB) ( 555 )

    The structure of Mesozoic in Chaoshan sag in the north of the South China Sea is quite complex,so two-dimensional seismic data imaging can not accurately reveal the inside of the structure,and the environment in this area is complex and not suitable for conventional multi-cable three-dimensional seismic data acquisition system.Based on the characteristics of quasi three dimensional seismic data acquisition by single source and single long streamer system,the authors used air-gun de-bubble technology in combination with multiple suppression method,Compact Fourier Interpolation technology and three-dimensional prestack time migration technology in the seismic data processing project.It is for the first time that three-dimensional prestack time migration data were obtained in this area,and the quality of the imaging profile is greatly improved relative to that of the two-dimensional data.It can accurately reveal the inner curtain of the thrust structure and solve the problem that can not be solved by the former two-dimensional seismic exploration.

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    The application of reverse time migration to GPR data processing
    Jun-Bo GONG, Hong-Hua WANG, Min-Ling WANG, Ze-Ming LUO
    Geophysical and Geochemical Exploration. 2019, 43 (4): 835-842.   DOI: 10.11720/wtyht.2019.1319
    Abstract   HTML ( 5 )   PDF (2734KB) ( 773 )

    As a shallow geophysical detection technology,Ground Penetrating Radar (GPR) has been widely used in engineering detection.In order to improve the interpretation accuracy of radar data,this paper introduces reverse time migration (RTM) to process and interpret GPR observed data.Firstly,Finite Difference Time Domain (FDTD) equations of electromagnetic wave in two-dimensional TM mode,CFL numerical stability condition and dispersion relations are derived from Maxwell equations.On such a basis,the principle of RTM and the formula of zero time imaging condition are elaborated,and the corresponding program of RTM is compiled.Two typical voids models are established.The simulated data of two typical void GPR models are processed by RTM to verify the validity of GPR RTM in improving imaging resolution.Compared with Kirchhoff migration result,the homing of reflected wave is more accurate and the convergency of diffracted wave is more complete in the RTM image.Finally,RTM is applied to processing the observed data,which is observed on the underground pipeline.The pipeline is accurately delineated,which provides a scientific basis for the follow-up construction and disposal of the road.

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    Automatic first-breaks picking based on region growing method
    Bai-Hong LIU, Zhi-Dong SHAO, Si-Lian ZHENG, Zhi-Xiang SONG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 843-850.   DOI: 10.11720/wtyht.2019.1428
    Abstract   HTML ( 2 )   PDF (8927KB) ( 522 )

    This paper presents a new method to pick the seismic first arrival automatically.First,local attributes such as local standard deviation and local cross-correlation are computed from one trace of shot record.The local attributes are calculated within moving windows along the seismic trace,so that local attributes traces are produced.Then region growing method is used to identify the valid signal region and noise signal region based on the local attributes traces.The location of the edge of the identified two regions can be considered as the first breaking time of the seismic trace.The method has been tested on real data sets,and the results show that,with an appropriate tuning of its parameters,the method is robust under noisy conditions,computationally efficient,and easy to apply.

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    Seismic reflectivity inversion based on L1-L1-norm sparse representation
    Zhan-Zhan SHI, Yan-Qing XIA, Huai-Lai ZHOU, Yuan-Jun WANG, Xiang-Rong TANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 851-858.   DOI: 10.11720/wtyht.2019.1390
    Abstract   HTML ( 3 )   PDF (4169KB) ( 482 )

    High-resolution seismic inversion is confronted with two problems:First,seismic inversion is an ill-posed problem and has multiplicity of solutions,and second,noise and distortion are generated in the flows of acquisition and processing to reduce the stability of the inversion algorithm.Aimed at solving these two problems, this paper proposes an inversion method of seismic reflectivity based on L1-L1-norm sparse representation.Firstly,the L1-norm regularization term is used to reduce the inversion multiplicity,and then the L1-norm fitting term is used to enhance the noise robustness.The wavelet is extracted by well logging and seismic data to construct the over-complete wedge wavelet dictionary,and then the seismic signal is sparsely decomposed by the L1-L1-norm sparse representation,so as to realize the high-resolution reflectivity inversion.The experimental results of wedge model and actual seismic data show that the inversion algorithm is stable and has good noise robustness,and the inversion results are accurate and credible through logging data calibration.

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    A study of influence of fracture connectivity on wave propagation characteristics
    Jie TANG, Cong LI, Lei WEN, Rui-Xuan QI
    Geophysical and Geochemical Exploration. 2019, 43 (4): 859-865.   DOI: 10.11720/wtyht.2019.1417
    Abstract   HTML ( 4 )   PDF (4286KB) ( 460 )

    The underground medium is affected by multi-stage tectonic movement,the phenomenon that the crack exists in multiple groups is common,and the connectivity between multiple sets of fractures will affect the elastic parameters of the medium.When the elastic modulus of a saturated rock with two sets of staggered fractures are calculated,in the case where the fracture is connected,the elastic parameters of the dry rock are calculated first,and then the elastic parameters of the fluid-containing fracture medium are obtained by anisotropic fluid replacement.In the case of non-intersecting fractures,first the saturated crack toughness is calculated for the two sets of fractures,and then the overall elastic parameters of the saturated fractured rock are calculated.Some conclusions have been reached:①Under oil-water saturation conditions,when the fractures are connected,the shear-wave splitting parameters change less with the increase of oil saturation;when the fracture is not connected,the shear wave splitting parameter changes greatly with the increase of oil saturation.②As the crack inclination angle θ increases,the shear wave splitting parameter decreases.③Under oil saturation conditions,shear wave splitting parameters increase slightly with increasing porosity when the fractures are connected;when the fracture is not connected,the shear wave splitting parameter decreases with the increase of porosity,and the degree of reduction is relatively large.

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    Influence of near surface structure on multi-wave exploration at the mountain front of South Junggar Basin
    Zhi-Guo CHENG, Ting-Ting HU, Ling-Yun WEI, Hai-Yang GUO
    Geophysical and Geochemical Exploration. 2019, 43 (4): 866-871.   DOI: 10.11720/wtyht.2019.1357
    Abstract   HTML ( 4 )   PDF (7054KB) ( 417 )

    In Junggar basin,near surface structure is an obvious factor influencing seismic data.2D 3C seismic line data were collected recently at Gaoquan anticline of the mountain front area.Nevertheless,S/N of PS-wave section was obviously lower than P-wave section at the east end of 2D line.To verify and analyze near surface structure's influence on multi-wave 3C seismic data,the authors built forward model by using its near surface structure and well-logging data so as to get modeling shots with real acquisition geometry.By analysis of modeling results and near surface structure investigation,it is found that the thickness of low velocity layer increases and Xiyu conglomerates are developed at the east end of 2D line because of Kuitun River's sedimentation,which is the main reason of energy and S/N reduction of multi-wave seismic data.It is also proved that PS wave is more easily influenced by near surface structure's attenuation than P wave.

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    Research and implementation of data processing method for the three-axis stabilized platform airborne gravity measuring system
    Feng LUO, Guan-Xin WANG, Xi-Hua ZHOU, Xing-Su LI
    Geophysical and Geochemical Exploration. 2019, 43 (4): 872-880.   DOI: 10.11720/wtyht.2019.0052
    Abstract   HTML ( 5 )   PDF (2957KB) ( 462 )

    It is of great significance to study the data-processing methods of airborne gravity survey, improve the accuracy of data processing and catch up with the advanced world level. In this paper, based on the domestic three-axis stabilized platform airborne gravity measurement system, the authors carried out the research on data processing methods and corresponding software development of airborne gravity measurement and realized the Kalman smoothing algorithm suitable for the stabilized platform airborne gravity data. The platform airborne gravity anomaly was solved for the first time in China. The internal coincidence accuracy reached 0.590×10 -5m/s 2, the external coincidence (GT airborne gravity measuring system) accuracy reached 0.581×10 -5m/s 2, and the accuracy of data processing was up to the international advanced level. The results show that the data processing method is feasible, has high precision, and can improve the data-processing technology of airborne gravity survey in China.

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    The application of aeromagnetic three-component upward continuation to recognizing physical parameters of geological body
    Xi-Zi LI, Hua GUO, Song HAN, Hao-Jun LIU, Qiang ZHENG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 881-891.   DOI: 10.11720/wtyht.2019.1385
    Abstract   HTML ( 4 )   PDF (4132KB) ( 735 )

    China developed the aeromagnetic three-component measurement system in 2017; nevertheless, the application of the three-component data is still in the exploratory stage. At first, the authors derived the upward continuation formula of magnetic three-component data and obtained the formula for the first time. Then the authors designed cube combinational models, with depth of center point ,volume, magnetization in different depths and depth of top surface as the variables. The relationship between minimum continuation height and physical parameters was obtained. In addition, the authors summarized some laws from these models. Finally, these conclusions were combined with the actual aeromagnetic three-component data. According to the geological condition of the survey area, the interpretation was made and good results were obtained.

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    The application of orthogonal polynomial fitting method to airborne electromagnetic motion noise removal
    Wei HUANG, Fang BEN, Shan WU, Si-Yuan SUN, Gui-Xiang LIAO, Yong-Zai XI
    Geophysical and Geochemical Exploration. 2019, 43 (4): 892-898.   DOI: 10.11720/wtyht.2019.0086
    Abstract   HTML ( 2 )   PDF (4480KB) ( 373 )

    Time domain airborne electromagnetic measurement data are often accompanied by motion noise with low-frequency characteristics, whose amplitude is much stronger than the magnetic field intensity of the airborne electromagnetic response. Therefore, whether it can be removed correctly and efficiently has become a key technology in the pre-processing of airborne electromagnetic data in time domain. In this paper, orthogonal polynomial fitting method is used to remove the motion noise of airborne electromagnetic data in time domain. The orthogonal polynomials fitting method is used to fit each half-cycle time series so as to remove the motion noise. It can be seen from the result of removing motion noise from simulation data and real data that orthogonal polynomials fitting method can effectively remove motion noise, improve the quality of airborne electromagnetic real data, and improve the SNR of data.

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    A study of landmine target recognition based on Mahalanobis distance template feature
    Cheng-Hao WANG, Dan-Dan CHENG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 899-903.   DOI: 10.11720/wtyht.2019.1363
    Abstract   HTML ( 2 )   PDF (1371KB) ( 482 )

    Mine detection by ground penetrating radar is an important application direction, and its detection effect on non-metallic mines or mines with low metal content is remarkable. In this paper, aimed at tackling the problem that the target feature extraction is difficult when the ground penetrating radar detects the mine, the authors propose the SVM recognition algorithm based on the Mahalanobis distance template feature and give the recognition result. This method can effectively extract the target characteristics of mines, and is helpful to data interpretation of ground penetrating radar and recognition and location of mine targets.

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    Characteristics of selenium content in soil of eastern Baoqing County and its relationship with soil properties
    Yue-Ping WANG, Li ZHANG, Yu-Jun CUI, Shi-Jia LYU
    Geophysical and Geochemical Exploration. 2019, 43 (4): 904-911.   DOI: 10.11720/wtyht.2019.0037
    Abstract   HTML ( 5 )   PDF (2067KB) ( 677 )

    In order to study the soil selenium content in the eastern part of Baoqing County and its relationship with soil properties, the authors collected 17 470 soil samples in the depth of 0~20 cm from the main agricultural areas in eastern Baoqing County according to the density of 4 points/km 2. Physical and chemical indicators such as selenium content, organic carbon and pH were analyzed. The results show that the selenium content in the topsoil is between 0.01×10 -6 and 1.17×10 -6, the average content is 0.326×10 -6, 73.53% of the soil is selenium-sufficient, 21.14% of the soil is selenium-abundant, and 4.56% of soil is of potential selenium-deficiency. Selenium-deficient soil only accounts for 0.77%, and there is no selenium poisoning area. The average content of selenium in different soil parent materials is arranged in decreasing order of alluvial deposits>alluvial deposits>granite>sedimentary rocks>basic-neutral volcanic rocks; the average content of selenium in different soil types in arranged in decreasing order of albic soil>meadow soil>black soil>marshy soil>dark brown soil>paddy soil; the average content of selenium in different land use is arranged in decreasing order of irrigated farmland>dry farmland>grassland>construction land>unused land>forest land. Correlation analysis shows that soil organic carbon (TOC) and pH are the main factors affecting the selenium content in the surface soil of the study area.

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    Magnetic susceptibility distribution characteristics and environmental records along red clay section in Hunan-Jiangxi hilly area
    Ping-Sheng XIONG, Shu-Rong LIU, Yang-Yang GUO
    Geophysical and Geochemical Exploration. 2019, 43 (4): 912-918.   DOI: 10.11720/wtyht.2019.1454
    Abstract   HTML ( 3 )   PDF (1071KB) ( 560 )

    The red earth in southern China has been generally considered potential paleoenvironmental record. In order to reveal the paleoenvironmental implications of the red clay profile in southern China and its relationship with chemical index of alteration (CIA), the authors measured magnetic susceptibility and chemical elements of two hundred and sixty-three samples collected from Huangjin (HJ) ,Shahe (SH), Tiancun (TC), Gaoxing (GX), Songmu (SM) in Xianggan area. Some conclusions have been reached: (1) The average magnetic susceptibility of the vermiculated red clay layer is higher than that of homogeneous red clay layer and red soil layer in Gannan region. The low frequency magnetic rate of granite clay in Gannan region is higher than that of granite clay in Hengyang region. The distribution ranges of the low frequency magnetic susceptibility of red clay sections vary from 12.1×10 -8 m 3/kg to 463.91×10 -8 m 3/kg;(2)There is still preferable relationship between the low frequency magnetic susceptibility and chemical index of alteration (CIA) in Hengyang region. The high magnetic susceptibility values correspond to the high CIA values, indicating a warm and humid envirenment; the low magnetic susceptibility values correspond to the low CIA values, indicating a cold and dry envirenment.(3)The low-frequency magnetic susceptibility curves are regionally different in frequency and amplitude, the low frequency magnetic susceptibility of the red clay section shows a consistent downward trend, which reveals the change trend of palaeoclimate from warm-wet to warm-dry during the red clay deposition period.

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    The detection of grouting compactness of pre-stressed ducts based on the impact-echo method
    Guang-Zhen QU, Guang-Li ZHOU, Ke-Chao ZHANG, Yan-Wei WANG
    Geophysical and Geochemical Exploration. 2019, 43 (4): 919-924.   DOI: 10.11720/wtyht.2019.1098
    Abstract   HTML ( 3 )   PDF (1804KB) ( 591 )

    A detailed description of impact-echo method was given firstly,then four different situations of grouting quality were modified from empty to dense through making test model.After that,the impact-echo method was adopted to detect the grouting quality of tendon ducts.The study was summarized as follows:If the reflection time of slab bottom and nominal thickness of slab increased,the degree of density would increase;the reflection time and nominal thickness of slab was the biggest when testing was from half-hole of web.At the same time,the reflection time of compacted and uncompacted tendon ducts was basically the same.In the end,the uncompacted parts of the prestressed pipe grouting were put forward.The method was verified by the engineering project and was proved to be of reference value.

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