The nonferrous metal mines in China are rapidly depleting due to years of mining, and it has become difficult to identify new mineral resources in the periphery of the old mining area. In order to deal with this situation, advanced technologies and equipment must be deployed. The borehole transient electromagnetic method (TEM) has become a key technology due to its deep investigative capabilities within conductive geological structures. In the present study, in order to meet the exploration needs at depths of less than 3000 m, surface-borehole TEM exploration was used to analyze the characteristics of electromagnetic signals generated by a long wire source and a large loop source, providing essential data for the development of key technologies, such as sensor parameter design and signal gain optimization of the TEM system in the borehole. This study discussed in detail two key technical problems as follows: firstly, the efficient synchronization mechanism between the ground transmitter system and the borehole electromagnetic signal acquisition system ensured the accuracy and timeliness of data acquisition; and secondly, the realization of mass storage technology, which effectively solved the problem of mass storage and real-time transmission of data in a deep borehole environment. The effectiveness of the surface-borehole TEM systems with a long wire source and a large loop source was verified by tests in real mines. The surface-borehole electromagnetic signal acquisition system developed in this study effectively collected electromagnetic signals in the borehole, and the results accurately reflected the stratigraphic information of mineral resources in the study area. This study can pave a new technical path for the exploration of deep and peripheral areas of non-ferrous metal mines and provide valuable experience and insights for mineral resource exploration in similarly complex geological environments.

With the rapid development of the economy, the demand for mineral resources has increased dramatically. Because it is difficult to explore new mines in deep and peripheral areas, new theories, technologies, methods, and equipment are needed. How to accurately and effectively carry out new mine exploration has become an urgent research topic. In this study, based on the requirements of mine exploration within a depth of 3000 m, an array receiver for borehole-induced polarization was developed. Each channel of the receiver array independently acquires data, and it is able to carry out full waveform acquisition in the dual voltage and voltage difference mode. The structure of the receiver array can be flexibly adjusted to obtain array observations of induced polarization in different ways. Experiments demonstrated that the device works well at a high temperature of 155 °C, its resolution reached 0.1 μV, and the error between the different channels was less than 3%. Its dynamic range is 180 db. Through experiments on induced polarization in a demonstration mining area, the apparent resistivity curve and the apparent polarization curve were determined to be consistent with the known well-logging information, and the interpretation results were in agreement with the stratum information.

When encountering sedimentary rocks with obvious laminations or fracture development zones, the conductivity of the conductive medium in different directions will change significantly, and the subsurface medium will exhibit macroscopic conductivity anisotropy. To analyze the impact of electrical anisotropy on the surface–borehole transient electromagnetic exploration method, we used the finite element method to investigate the electrical anisotropy surface–borehole transient electromagnetic three-dimensional (3D) forward algorithm, in which we used a tetrahedral mesh to spatially discretize the time–domain Maxwell equation. Then, we discretized it using the second-order backward Eulerian difference method, and we obtained the fields through the PARDISO solver. The validity and correctness of the algorithm were verified through comparison of a one-dimensional (1D) anisotropic model, a complex three-dimensional (3D) isotropic model, and a three-dimensional (3D) anisotropic half-space model. A typical anisotropic geological model was constructed to analyze the effects of anisotropic strata and anomalies in the different principal axis directions on the surface–borehole transient electromagnetic response. The results show that the response of the anisotropic medium is related to the direction of the transmitting source, and the response pattern is complex and volatile. The electrical anisotropic anomaly does affect the amplitude, which should be given special attention when performing surface–borehole transient electromagnetic inversion interpretation.

The surface–borehole transient electromagnetic method (TEM) employs surface-based transmission and downhole reception to collect electromagnetic data. This configuration offers distinct advantages over traditional TEM approaches by effectively attenuating surface electromagnetic noise and cultural interference, leading to enhanced signal strength and vertical resolution. As a result, it has emerged as a key technique for the exploration of deep mineral resources. Although a relatively comprehensive three-dimensional (3D) theoretical system for surface–borehole TEM has been established, most existing studies remain focused on forward modelling, with inversion interpretation receiving comparatively limited attention. In this study, a one-dimensional (1D) inversion algorithm for surface–borehole TEM data is developed. The approach begins with forward modelling based on numerical simulation, followed by the integration of a prior model to formulate an objective function. Optimization is carried out using the Broyden–Fletcher–Goldfarb–Shanno (quasi-Newton) method. A parameter transformation approach was further applied to convert the constrained inversion into an unconstrained optimization problem. The effectiveness of the proposed algorithm is validated through inversions performed on synthetic data derived from theoretical models. This method offers a reliable interpretation tool for practical surface–borehole TEM applications and provides a theoretical basis for the design and optimization of related instrumentation.

The frequency-domain controlled-source electromagnetic method (CSEM) has been widely used in fields such as oil and gas and mineral resource exploration. In areas with a significant IP response, the CSEM signals will be modified by the IP response of the subsurface. Accurately extracting resistivity and polarization information from CSEM signals may significantly improve the exploration interpretations. In this study, we replaced real resistivity with the Cole–Cole complex resistivity model in a forward simulation of the CSEM to obtain electric field responses that included both induced polarization and electromagnetic effects. Based on this, we used the adaptive differential evolution algorithm to perform a 1-d inversion of these data to extract both the resistivity and IP parameters. Inversion of the electric field responses from representative three-layer geoelectric models, as well as from a more realistic seven-layer model, showed that the inversions were able to effectively recover resistivity and polarization information from the modeled responses, validating our methodology. The electric field response of the real geoelectric model, with 20% random noise added, was then used to simulate actual measured CSEM signals, as well as subjected to multiple inversion tests. The results of these tests continued to accurately reflect the resistivity and polarization information of the model, confirming the applicability and reliability of the algorithm. These results have significant implications for the processing and interpretation of CSEM data when induced polarization effects merit consideration and are expected to promote the use of the CSEM in more fields.