Influence of induced polarization effects on AMT forward modeling and its numerical simulations for sandstone uranium deposits
HU Ying-Cai1,2,3(), WANG Rui-Ting1,2, LI Xiu2
1. Northwest Nonferrous Geological and Mining Group Co., Ltd., Xi’an 710054, China 2. School of Geological Engineering and Geomatics, Chang’an University, Xi’an 710061, China 3. Key Laboratory of Uranium Resource Exploration and Evaluation Technology, China National Nuclear Corporation, Beijing Research Institute of Uranium Geology, Beijing 100029, China
The extensively applied audio magnetotellurics (AMT) has become a primary method for deep geophysical exploration of solid mineral resources. However, its data processing and interpretation often only consider electromagnetic effects but ignore induced polarization (IP) effects, which is inconsistent with actual geological conditions. Based on the two-dimensional AMT finite-element forward modeling with IP effects, this study simulated the magnitude and regularity of the influence of various parameters of IP effects on the two-dimensional forward response. Moreover, this study conducted a numerical simulation on the geoelectric model of sandstone uranium deposits in the Erlian Basin. The results show that: (1) With an increase in the values of polarizability, frequency correlation coefficient, and time constant, the two-dimensional AMT forward modeling with IP effects based on the Cole-Cole model primarily reduced the abnormal response value of two-dimensional forward modeling apparent resistivity and increased the abnormal response value of impedance phase. This is beneficial for detecting low-resistivity targets rather than high-resistivity targets; (2) The zero-frequency resistivity and polarizability in IP effects exhibit a significant influence on the two-dimensional forward response. The influence of both frequency correlation coefficient and time constant on the forward response primarily depends on the polarizability. High polarizability suggests their significant influence on the forward response; (3) In the case of disseminated and sulfide-bearing lithologies in the sand bodies of sandstone uranium deposits, greater IP effects will significantly influence the detection of target sand bodies using frequency-domain AMT. Therefore, forward modeling is necessary before detection to determine the magnitude of IP effects.
胡英才, 王瑞廷, 李貅. 激电效应对AMT正演的影响及其在砂岩型铀矿中的数值模拟[J]. 物探与化探, 2024, 48(4): 1006-1017.
HU Ying-Cai, WANG Rui-Ting, LI Xiu. Influence of induced polarization effects on AMT forward modeling and its numerical simulations for sandstone uranium deposits. Geophysical and Geochemical Exploration, 2024, 48(4): 1006-1017.
Tang J T, Zhang L C, Wang X Y, et al. Subsurface electrical structure of the Fanshan-JiangjunmiaoRegion in the Lujiang-Zongyang Ore District derived from 3D inversion of audio-magnetotelluric data[J]. Chinese Journal of Geophysics, 2018, 61(4):1576-1587.
Wang J L, Di B Y, Zhang B S, et al. The application of audio frequency magnetotelluric method to the geothermal exploration:A case study of HuangniqiaoArea,Ninghua County,Fujian Province[J]. Geophysical and Geochemical Exploration, 2021, 45(3):576-582.
Wu Y, Guo J Q. The effect of audiomagnetotelluric sounding prospecting for detecting hydrogeological characteristic in takelamgan desert[J]. Chinese Journal of Engineering Geophysics, 2004, 1(3):269-273.
Zhang J, Chen X B, Yin X K, et al. 3D AMT array exploration in the selaha fault and adjacent area[J]. Earth Science, 2022, 47(3):856-866.
[7]
Jiang W P, Brodie R C, Duan J M, et al. Probabilistic inversion of audio-frequency magnetotelluric data and application to cover thickness estimation for mineral exploration in Australia[J]. Journal of Applied Geophysics, 2023, 208:104869.
[8]
Xu Z M, Li G, Xin H C, et al. Hydrogeological prospecting in the Da Qaidam Area of the Qaidam Basin using the audio-frequency magnetotelluric method[J]. Journal of Applied Geophysics, 2020, 182:104179.
[9]
Maryadi M, Mizunaga H. Subsurface temperature estimation in a geothermal field based on audio-frequency magnetotelluric data[J]. Exploration Geophysics, 2022, 53(3):275-288.
Wan W, Tang X G, Huang Q H. Influence of induced polarization effects on 3D land CSEM sounding[J]. Progress in Geophysics, 2019, 34(6):2328-2335.
[11]
Pelton W H, Ward S H, Hallof P G, et al. Mineral discrimination and removal of inductive coupling with multifrequency IP[J]. Geophysics, 2012, 43(3):588-609.
[12]
Ware G H. Theoretical and field investigations of telluric currents and induced polarization[M]. Berkeley: University of California at Berkeley, 1974.
Tang J T, Huang L, Yu C L, et al. There sponsibility of apparent resistivity curves on CSAMT for polarized layer[J]. Chinese Journal of Engineering Geophysics, 2008, 5(6):648-651.
Yue A P, Di Q Y, Wang M Y, et al. 1D forward modeling of the CSAMT signal incorporating IP effect[J]. Chinese Journal of Geophysics, 2009, 52(7):1937-1946.
Fu C, Li W W, Li Z Y, et al. Inducedpolarization effect of magnetotelluric with polarized horizontal layers based on the Cole-Cole model[J]. Progress in Geophysics, 2016, 31(2):501-507.
Li Y, Lin P R, Xiao Y, et al. Induced Polarization effect on frequency-domain electromagnetic sounding with electric dipole source[J]. Chinese Journal of Geophysics, 2011, 54(7):1935-1944.
Xu K J, Shi S H, Zhou J H. Study on induced polarization effect of three dimensional magnetotelluric[J]. Northwestern Seismological Journal, 2009, 31(1):31-34,85.
[20]
付振兴. 考虑激电效应的大地电磁三维正反演研究[D]. 北京: 中国地质大学(北京), 2018.
[20]
Fu Z X. Research of the three-dimensional magnetotelluric inversion with induced polarization effect[D]. Beijing: China University of Geosciences(Beijing), 2018.
[21]
黄逸伟. 含激电效应的可控源电磁法三维正演及响应研究[D]. 抚州: 东华理工大学, 2017.
[21]
Huang Y W. 3D forward modeling and response analysis of the controlled source electromagnetic signal with IP effect[D]. Fuzhou: East China Institute of Technology, 2017.
[22]
Vozoff K. Electromagnetic methods in applied geophysics[J]. Surveys in Geophysics, 1980, 4(1/2):9-29.
[23]
徐世浙. 地球物理中的有限单元法[M]. 北京: 科学出版社, 1994.
[23]
Xu S Z. FEM in Geophysics[M]. Beijing: Science Press, 1994.
[24]
胡英才. 矢量有限元三维张量CSAMT正演模拟研究[D]. 长春: 吉林大学, 2015.
[24]
Hu Y C. Three dimensional tensor controlled source electromagnetic modeling based the vector finite element method[D]. Changchun: Jilin University, 2015.
Li Z Y, Qin M K, Fan H H, et al. Main progresses of uranium geology and exploration techniques for the past decade in China[J]. Bulletin of Mineralogy,Petrology and Geochemistry, 2021, 40(4):845-857,1001.
Hu Y C, Zhang R L, Wang H. Simulation and application of broadband magnetotelluric sounding for sandstone type uranium deposits in yihegaole area[J]. Uranium Geology, 2020, 36(5):432-440,476.
Wang H, Hu Y C, Zhang R L. Feasibility of extracting polarization information from MT data in uranium exploration[J]. Uranium Geology, 2021, 37(2):269-275.
