| Citation: |
Peng-liang Yu, Ting Qu, Ri-zheng He, Jian-li Liu, Su-fen Wang, Xiao-long Chen, 2023. Application of tensor CSAMT with high-power orthogonal signal sources in Jiama porphyry copper deposit, South Tibet, China Geology, 6, 37-49. doi: 10.31035/cg2021065
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Application of tensor CSAMT with high-power orthogonal signal sources in Jiama porphyry copper deposit, South Tibet
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Abstract
The Jiama porphyry copper deposit in Tibet is one of the proven supergiant copper deposits in the Qinghai-Tibet Plateau at present, with the reserves of geological resources equivalent to nearly 20×106 t. However, it features wavy and steep terrain, leading to extremely difficult field operation and heavy interference. This study attempts to determine the effects of the tensor controlled-source audio-magnetotellurics (CSAMT) with high-power orthogonal signal sources (also referred to as the high-power tensor CSAMT) when it is applied to the deep geophysical exploration in plateaus with complex terrain and mining areas with strong interference. The test results show that the high current provided by the high-power tensor CSAMT not only greatly improved the signal-to-noise ratio but also guaranteed that effective signals were received in the case of a long transmitter-receiver distance. Meanwhile, the tensor data better described the anisotropy of deep geologic bodies. In addition, the tests also show that when the transmitting current reaches 60 A, it is still guaranteed that strong enough signals can be received in the case of the transmitter-receiver distance of about 25 km, sounding curves show no near field effect, and effective exploration depth can reach 3 km. The 2D inversion results are roughly consistent with drilling results, indicating that the high-power tensor CSAMT can be used to achieve nearly actual characteristics of underground electrical structures. Therefore, this method has great potential for application in deep geophysical exploration in plateaus and mining areas with complex terrain and strong interference, respectively. This study not only serves as important guidance on the prospecting in the Qinghai-Tibet Plateau but also can be used as positive references for deep mineral exploration in other areas.
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References
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Peng-liang Yu, Ting Qu, Ri-zheng He, Jian-li Liu, Su-fen Wang, Xiao-long Chen, 2023. Application of tensor CSAMT with high-power orthogonal signal sources in Jiama porphyry copper deposit, South Tibet, China Geology, 6, 37-49. doi: 10.31035/cg2021065
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Figure 1.
Geologic map of the Jiama porphyry copper deposit and the location of research section. a‒geotectonic outline map of Tibet; b‒geologic map of the Jiama porphyry copper deposit (1:50000).
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Figure 2.
Diagram of measurement range and observation means of tensor CSAMT.
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Figure 3.
Comparison of test curves in the case of different transmitter-receiver distances.
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Figure 4.
Comparison of test curves in the case of different emission currents.
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Figure 5.
Comparison of test curves in the case of different MN electrode spacing.
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Figure 6.
Comparison of test curves in the case of different observation duration.
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Figure 7.
Diagram of source and receiving devices of the high-power tensor CSAMT applied in the Jiama porphyry copper deposit..
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Figure 8.
Histograms for resistivity measurement of main rocks in the Jiama porphyry copper deposit.
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Figure 9.
Comparison of CSAMT curves collected in the case of different transmitting and receiving directions.
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Figure 10.
2D inversion results of four sets of high-power tensor CSAMT data along section BB’. a‒EW-direction transmitting and NS-direction receiving; b‒EW-direction transmitting and EW-direction receiving; c‒NS-direction transmitting and NS-direction receiving; d‒NS-direction transmitting and EW-direction receiving.
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Figure 11.
Comparison of 2D inversion results of tensor CSAMT and MT data of sections AA’ and BB’. a‒2D CSAMT inversion results of section AA’; b‒2D MT inversion results of section AA’; c‒2D CSAMT inversion results of section BB’; d‒2D MT inversion results of section BB’; JMKZ is a scientific borehole with a depth of 3000 m (see Fig. 1 for its location). Vertical variation of resistivity along JMKZ borehole see Fig. 12.
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Figure 12.
Histogram and curves obtained from core specimen measurement of JMKZ borehole, and inverted resistivity variation across JMKZ from MT and CSAMT of sections AA’ and BB’ in Fig. 11. a‒measured resistivity in JMKZ Borehole; b‒measured polarizability in JMKZ Borehole; c‒inverted 1D CSAMT curve of section AA’; d‒inverted 1D MT curve of section AA’; e‒inverted 1D CSAMT curve of section BB'; f‒inverted 1D MT curve of section BB’. Those location for (c), (d), (e), and (f) see successively (a), (b), (c) and (d) in Fig. 11.