Primary study on transient electromagnetic induced polarization effects of deep-sea polymetallic sulfides
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摘要: 瞬变电磁法是深海多金属硫化物勘探的有效手段。海底多金属硫化物中高品位的金属组分会引起极强的激电效应，且对瞬变电磁响应产生显著影响。本文通过实验室测量和数值模拟对深海多金属硫化物的激电效应进行了探讨和分析。首先对西南印度洋中脊热液区的岩矿石样品进行了较为系统的电性测试，典型硫化物的复电阻率在频率域有最大达160 mrad相位移动，时间域与频率域的测量结果表明，极化率参数可以很好地区分硫化矿物与围岩。利用Cole-Cole模型对实测复电阻率进行解释，得到复电阻率的特征参数，分析各参数与块状硫化物组分和结构的关系，并根据极化率参数对典型硫化物进行了分类。将典型硫化物的激电参数用于计算层状介质的瞬变电磁响应，计算结果表明，在海底多金属硫化物矿床瞬变电磁法响应的最佳观测时窗内可同时观测到激电效应的影响。虽然在采集时窗晚期瞬变响应发生畸变，但在信号接收早期，激电效应能有效增强瞬变电磁法对深海多金属硫化物的探测能力，为瞬变电磁实测数据提供解释依据。
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关键词:
- 瞬变电磁法 /
- 激电效应 /
- Cole–Cole模型 /
- 深海多金属硫化物
Abstract: Transient electromagnetic method (TEM) is an effective method for deep-sea polymetallic sulfide exploration. High-grade metal components in seafloor polymetallic sulfides cause extremely strong induced polarization effects and have a significant impact on transient electromagnetic response. In this paper, the inductive effects of deep-sea polymetallic sulfides were analyzed through laboratory measurement and numerical simulation. First, systematic electrical tests were carried out on rock ore samples from the hydrothermal vent fields on the southwest Indian Ocean Ridge. The complex resistivity of typical sulfides has a phase shift of up to 160 mrad in the frequency domain. The time domain and frequency domain measurements show that the polarizability parameter is a good indicator to distinguish sulfide minerals and surrounding rocks. Using the Cole-Cole model to interpret the complex resistivity to obtain the characteristic parameters of complex resistivity, the relationship between parameters and the composition and structure of the massive sulfide was analyzed, and the typical sulfides were classified based on the polarizability parameter. The induced polarization parameters of the typical sulfides were used to calculate the transient electromagnetic response of the layered medium, which show that the influence of induced polarization effect can be observed simultaneously in the best observation window of the TEM response of the deep-sea polymetallic sulfide deposit. Although the transient response is distorted in the late stage of the acquisition window, in the early stage of signal reception, the induced polarization effect effectively enhances the detection capability of the TEM for deep-sea polymetallic sulfides, which provides an explanation basis for the transient electromagnetic measurement data. -
图 1 西南印度洋脊玉皇热液区及龙旂热液区采样点分布
红色五角星代表块状硫化物采样点，黑色圆点代表围岩采样点；BTJ代表布韦三联点；SWIR代表西南印度洋脊；SEIR代表东南印度洋脊；CIR代表中印度洋脊；RTJ代表罗德里格斯三联点
Fig. 1 Distribution of the samples collected from Yuhuang hydrothermal vent field and Longqi hydrothermal vent field on the southwest Indian Ocean Ridge
The red stars represent the massive sulfide sampling stations and the black dots represent the surrounding rock sampling stations; BTJ represents Bouvet Triple Junction; SWIR represents Southwest Indian Ridge; SEIR represents Southeast Indian Ridge; CIR represents Central Indian Ridge; RTJ represents Rodrigues Triple Junction
图 2 不同岩性复电阻率特征。电阻率随频率变化（a），相位随频率变化（b）
Fig. 2 Different lithologic complex resistivity characteristics. Resistivity changes with frequency (a), phase changes with frequency (b)
图 3 本文实测复电阻率曲线与前人研究对比
SMS表示海底块状硫化物
Fig. 3 The measured complex resistivity curve in this study comparing with data from previous studies
SMS is seafloor massive sulfide
图 4 岩矿石激电特征与样品参数交会图
Fig. 4 Intersection diagram of induced polarization characteristics and sample parameters of rock ores
图 8 不同装置下含激电效应的瞬变电磁响应及其相对异常比值
dB/dt：感应电压
Fig. 8 Transient electromagnetic response and its relative anomaly ratio with induced polarization effects using different devices
dB/dt：induced voltage
表 1 岩矿石样品物性测量表
Tab. 1 Physical properties of rock ore samples
编号 岩性 样品 孔隙度
Φ饱和海水
ρ0/Ω·m饱和海水
充电率/mV·V–1复电阻率
虚部/S·m–1Φ平均值 ρ0平均值
/Ω·m9 含硫化物岩石（5块） 胶结硫化物角砾岩 15.56% 11.48 51.40 8.8×10–3 13.90% 9.88 57 胶结硫化物角砾岩 24.23% 18.54 49.58 8.1×10–3 61 块状硫化物 4.01% 11.61 72.07 1.0×10–2 62 块状硫化物 13.93% 5.45 99.12 3.7×10–2 63 块状硫化物 11.78% 2.33 112.20 5.3×10–2 213 矿化岩石（3块） 矿化蛋白石 7.60% 10.65 8.11 2.2×10–3 5.81% 59.12 217 矿化玄武岩 4.02% 128.71 50.58 5.8×10–4 241 矿化玄武岩 5.80% 38.00 10.48 5.0×10–4 1 玄武岩（23块） 玄武岩 6.38% 78.32 5.81 1.0×10–4 3.54% 308.25 7 玄武岩 8.52% 58.16 6.11 1.9×10–4 17 玄武岩 3.46% 242.79 7.34 3.3×10–5 21 玄武岩 2.25% 418.42 7.46 1.8×10–5 45 玄武岩 4.15% 123.90 6.90 6.3×10–5 69 玄武岩 4.94% 74.55 8.27 1.3×10–4 83 玄武岩 4.16% 114.06 9.63 9.2×10–5 89 玄武岩 3.36% 42.77 5.43 2.1×10–4 101 玄武岩 4.24% 52.08 7.06 2.0×10–4 105 玄武岩 3.06% 38.04 5.97 2.3×10–4 109 玄武岩 1.97% 579.47 7.56 1.4×10–5 113 玄武岩 4.69% 42.04 7.15 3.1×10–4 123 玄武岩 1.94% 158.59 6.37 2.5×10–5 129 玄武岩 0.82% 1537.10 7.05 5.5×10–6 137 玄武岩 2.43% 142.82 5.88 2.8×10–5 145 玄武岩 1.71% 238.30 7.34 6.0×10–5 165 玄武岩 2.02% 326.53 10.73 3.6×10–5 169 玄武岩 3.24% 76.20 4.79 7.7×10–5 201 玄武岩 2.28% 202.70 6.96 4.1×10–5 211 玄武岩 11.02% 27.84 9.17 8.0×10–4 221 玄武岩 3.86% 66.01 7.27 1.5×10–4 229 玄武岩 0.50% 1 261.00 37.30 4.2×10–5 267 玄武岩 0.51% 1 188.00 7.60 9.8×10–6 49 蚀变玄武岩（7块） 蚀变玄武岩 5.11% 108.93 6.92 5.7×10–5 6.74% 56.36 53 蚀变玄武岩 10.32% 31.49 9.53 5.6×10–4 147 蚀变玄武岩 3.40% 68.44 6.28 1.4×10–4 149 蚀变玄武岩 7.83% 26.82 9.27 7.6×10–4 
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表 2 硫化物物性及激电特征参数
Tab. 2 Physical properties and induced polarization effects characteristics of sulfides
编号 岩石类型 $\,\rho _{}^@1\;{\rm {Hz} }(\Omega \cdot {\rm m})$ 孔隙度/% $m$ $c$ $\tau $/s 9 胶结硫化物角砾岩 10.52 15.56 0.52 0.34 0.040 61 块状硫化物 13.10 4.01 0.63 0.38 23.418 62 块状硫化物 3.88 13.93 0.88 0.19 0.870 63 块状硫化物 2.19 11.78 – – 100.000 注：ρ@1 Hz（Ω·m）表示不同岩性电阻率大小的相对关系。
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