# Effective-Medium Inversion of Induced Polarization Data for Mineral Exploration and Mineral Discrimination: Case Study for the Copper Deposit in Mongolia

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## Abstract

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## 1. Introduction

## 2. Regularized Integral Equation (IE)-Based Inversion for Complex Resistivity

## 3. GEMTIP Resistivity Relaxation Model

## 4. Regularized Inversion for the GEMTIP Model Parameters

## 5. Fréchet Derivative Calculation Using the Quasi-Born Approximation

## 6. Calculation of the Fréchet Derivatives with Respect to the GEMTIP Model Parameters

## 7. Model Study of 3D Spectral IP Inversion in the Frequency Domain and in the Time Domain

- Resistivity of the background (homogeneous half-space): 100 $\mathrm{\Omega}\xb7$m
- GEMTIP parameters:
- -
- Grain size: $1\times {10}^{-4}$, $1\times {10}^{-5}$ m (major and minor radii of ellipsoidal grain)
- -
- DC resistivity: 5 $\mathrm{\Omega}\xb7$m
- -
- Fraction volume: 33% (Chargeability coefficient: 0.5)
- -
- Time constant: 1.0 s
- -
- Relaxation coefficient: 0.5

#### 7.1. 3D Inversion of Frequency-Domain IP Data

#### 7.2. 3D Inversion of Time-Domain IP Data

## 8. Case Study for the Copper Deposit in Mongolia

- (1)
- 3D inversions of IP data: to produce 3D models of the electrical properties (GEMTIP model parameters);
- (2)
- Petrophysical and mineralogical analyses of rock samples: to determine the relationship between geology/lithology and electrical properties;
- (3)
- Interpretation of the obtained results: to generate the images of the target mineralized zones (on deposit scale).

#### 8.1. 3D Inversion of IP Data

- Pole–Dipole IP survey (time domain)
- Total of 8 lines (numbered from 0 to 7, shown as blue dots in Figure 6)
- Transmitter: with two current electrodes (A and B); one of them (A) is located on the survey line, while another (B) is located far from the survey line.
- Spacing of two potential (receiver) electrodes (M and N, spacing a): 100 and/or 200 m.
- Period of the transmitting current: 2 s.
- Data acquisition: from 0.04 to 2 s after the transmitting current is turned off, with semi-logarithmic 20 time windows.

- Gradient IP survey (time-domain)
- Total 66-km line (shown as red dots in Figure 6); whole area was divided into three blocks.
- Transmitter: electric bipole with the length of 1.2 to 3 km.
- Spacing of two potential (receiver) electrodes: 50 m.
- Period of the transmitting current: 2 s ON, and 2 s OFF.
- Data acquisition: from 0.06 to 2 s after the transmitting current is turned off, with semi-logarithmic 20 time windows.

#### 8.2. Interpretation of the Target Mineralization Zones

## 9. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 2.**Vertical cross sections of the GEMTIP model parameters (DC anomalous conductivity, fraction volume, time constant, and relaxation parameter) recovered from the 3D inversion of frequency-domain SIP data.

**Figure 3.**Vertical cross sections of the GEMTIP model parameters (DC anomalous conductivity, fraction volume, time constant, and relaxation parameter) recovered from the 3D inversion of time-domain SIP data.

**Figure 6.**IP survey lines (pole–dipole and gradient arrays) in the survey area. The black rectangle shows the area with higher potential of mineralization, estimated from drilling results.

**Figure 7.**IP survey lines (Pseudo sections of the observed (top) and predicted (bottom) pole–dipole IP data; Line 1, time channel 5.

**Figure 9.**A 3D view of the 3D chargeability model recovered from 3D inversion of pole–dipole IP data.

**Figure 10.**A 3D view of the 3D time constant model recovered from 3D inversion of pole–dipole IP data.

**Figure 11.**A 3D view of the 3D relaxation parameter model recovered from 3D inversion of pole–dipole IP data.

**Figure 12.**A vertical cross section of the 3D resistivity model recovered from 3D inversion of the pole–dipole IP data along Line 1.

**Figure 13.**A vertical cross section of the 3D chargeability model recovered from 3D inversion of the pole–dipole IP data along Line 1.

**Figure 14.**A vertical cross section of the 3D time constant model recovered from 3D inversion of the pole–dipole IP data along Line 1.

**Figure 15.**A vertical cross section of the 3D relaxation parameter model recovered from 3D inversion of the pole–dipole IP data along Line 1.

**Figure 16.**A 3D cross plot between the chargeability, time constant, and relaxation parameter. The target mineralized zones can be specified using the range of red volume.

**Figure 19.**Vertical cross sections of the 3D interpreted target mineralized zones along (

**a**) section 1, (

**b**) section 2, (

**c**) section 3, (

**d**) section 4, and (

**e**) section 5 in Figure 18, with assay data.

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**MDPI and ACS Style**

Zhdanov, M.; Endo, M.; Cox, L.; Sunwall, D.
Effective-Medium Inversion of Induced Polarization Data for Mineral Exploration and Mineral Discrimination: Case Study for the Copper Deposit in Mongolia. *Minerals* **2018**, *8*, 68.
https://doi.org/10.3390/min8020068

**AMA Style**

Zhdanov M, Endo M, Cox L, Sunwall D.
Effective-Medium Inversion of Induced Polarization Data for Mineral Exploration and Mineral Discrimination: Case Study for the Copper Deposit in Mongolia. *Minerals*. 2018; 8(2):68.
https://doi.org/10.3390/min8020068

**Chicago/Turabian Style**

Zhdanov, Michael, Masashi Endo, Leif Cox, and David Sunwall.
2018. "Effective-Medium Inversion of Induced Polarization Data for Mineral Exploration and Mineral Discrimination: Case Study for the Copper Deposit in Mongolia" *Minerals* 8, no. 2: 68.
https://doi.org/10.3390/min8020068