Search Results (91)

Dixie Valley, located in west-central Nevada within the Basin and Range Province, is one of the most important geothermal systems in the western United States and an increasingly attractive target for critical-mineral exploration. The valley combines active extensional tectonics, major range-front and intrabasin fault systems, high heat flow, hydrothermal alteration, and thick sedimentary basins that may provide favorable conditions for the development of geothermal reservoirs and lithium-bearing brines or clays. This paper presents an integrated multiphysics interpretation of gravity, magnetic, helicopter-borne time-domain electromagnetic (HeliTEM), and magnetotelluric (MT) data from Dixie Valley, with emphasis on the Grover Point area investigated by the Basin and Range Investigation for Developing Geothermal Energy (BRIDGE) program. We apply joint Gramian inversion of gravity and magnetic data to recover mutually consistent density and magnetization models, including separate induced and remanent magnetization components. We also perform rigorous 3D inversion of HeliTEM data and cooperative 3D inversion of HeliTEM and MT data to obtain a resistivity model extending from the shallow basin fill to deeper fault-controlled geothermal structures. The integrated interpretation identifies low-density sedimentary basins, induced magnetization highs related to magnetic basement or intrusive rocks, remanent magnetization variations associated with basement architecture and hydrothermal alteration, and conductive corridors interpreted as clay-rich alteration zones and possible hydrothermal pathways. These results demonstrate that integrated gravity, magnetic, HeliTEM, and MT inversion can substantially reduce interpretation ambiguity and improve targeting of concealed geothermal systems and associated lithium resources in extensional terranes. Full article

The Songpan-Ganzi and Eastern Kunlun region on the northern margin of the Tibetan Plateau is a key area for the evolution of the Paleo-Tethys tectonic domain and hosts abundant gold, lithium, and polymetallic mineral resources. To reveal the deep structure of this region and its metallogenic background, this study constructed a lithospheric electrical structure model based on magnetotelluric (MT) data along a profile traversing tectonic units such as the Qiangtang, Songpan-Ganzi, and Eastern Kunlun blocks. Data processing, dimensionality analysis, and two-dimensional inversion were performed. The results show that a large-scale, funnel-shaped conductor, originating from the upper mantle and penetrating the middle-lower crust, exists beneath the Songpan-Ganzi and Qiangtang terranes, indicating a major channel for deep-seated thermal material upwelling. Driven by Cenozoic tectonic reactivation, the thermal materials ascended along pre-existing lithospheric weak zones formed during the closure of the Paleo-Tethys Ocean. It spread extensively within the upper-middle crust of the Songpan-Ganzi terrane and migrated to the Eastern Kunlun orogenic belt via complex fault systems, ultimately forming low-resistivity bodies that closely coincide with the locations of major shallow ore-controlling faults. This electrical model suggests the presence of a “thermal material channel” system extending from the mantle to the shallow crust. The study suggests that the migration pathways of ore-forming fluids, represented by gold deposits in the Eastern Kunlun metallogenic belt, are highly correlated with the fault-magma channel system constituted by intra-crustal conductors. In contrast, the lithium-rich granitic magmatism associated with lithium mineralization within the Songpan-Ganzi terrane may be related to the deep thermal background reflected by the large-scale conductor in the upper mantle. From the perspective of electrical structure, this study suggests that mineralization in this region may be closely linked to deep crust–mantle processes. The reactivation of pre-existing tectonic-magmatic channels by Cenozoic thermal material is key to controlling the distribution pattern of dominant shallow mineral resources. The research results provide important geophysical constraints for a deeper understanding of the tectonic–magmatic–mineralization coupling mechanism on the northern margin of the Tibetan Plateau. Full article

3D magnetotelluric (MT) inversion based on the Gauss–Newton (GN) framework plays an important role in deep mineral exploration by imaging subsurface electrical conductivity structures. However, large-scale 3D MT inversion remains computationally expensive due to the high cost of sensitivity-matrix construction. To address this challenge, we develop a stochastic Gauss–Newton (SGN) framework that reduces computational cost through random data subsampling while preserving the practical convergence behavior of GN inversion. In the proposed framework, only a randomly selected subset of data is used to approximate the GN search direction. By exploiting a key property of MT forward modelling, namely that responses at all receivers are obtained simultaneously for each frequency, the line search is performed using the full dataset, ensuring stable convergence of the inversion process. The SGN framework is validated using both a synthetic multiblock model and a field dataset from the Akebasitao area in Xinjiang, China. The recovered models remain highly consistent with those obtained using conventional full-data Gauss–Newton inversion across a wide range of sampling ratios. For the synthetic example, reducing the sampling ratio from 100% to 10% decreases peak memory consumption from approximately 433 GB to 242 GB and reduces runtime from 86.8 h to 23.9 h while maintaining comparable inversion quality. Similar computational savings are achieved for the field-data inversion. The field application successfully recovers the major conductive structures along the margins of the intrusion that are associated with hydrothermal alteration and fluid activity, highlighting the capability of SGN to delineate geologically meaningful targets relevant to deep mineral exploration. These results demonstrate that SGN provides an efficient and scalable approach for large-scale 3D MT inversion. Full article

On 4 February 1975, the Haicheng Ms 7.3 earthquake occurred in the Liaodong Uplift, northeastern China. To investigate its seismogenic structure and deep geological environment, we acquired broadband magnetotelluric data along two intersecting profiles across the epicentral region and performed three-dimensional inversion. Two orthogonal electrical sections were then extracted from the resulting 3D resistivity model to image the crustal structure beneath the Haicheng earthquake area. The model reveals that the northern segment of the Tanlu fault corresponds to a major electrical discontinuity between the Xialiaohe Basin and the Liaodong Uplift, suggesting that it may represent a deep-seated fault zone extending into the lithosphere. Beneath the Liaodong Uplift, a prominent mid-crustal low-resistivity layer is developed, and a synform conductive body is resolved beneath the source region. The Haicheng mainshock and relocated aftershocks are mainly distributed along the interface between this conductive body and the overlying high-resistivity upper crust. In addition, the Haichenghe–Dayanghe fault is imaged as a conductive zone that connects the mid-crustal conductor with shallower crustal levels. These electrical features suggest that deep crustal fluids, possibly related to Pacific Plate subduction and craton destruction, may have migrated upward along fault zones, weakened the seismogenic fault system, and promoted earthquake nucleation. Compared with the volcanic regions of the Jilin–Heilongjiang orogenic belt, where conductive anomalies extend into the upper mantle, the Haicheng region is characterized mainly by intracrustal conductors. This contrast highlights the role of crustal-scale conductive structures in the seismogenic environment of the Haicheng earthquake and provides geophysical constraints for comparing earthquake- and volcano-related deep processes in northeastern China. Full article

The study area is located within a fault-controlled sedimentary basin and hosts abundant evaporite resources, including gypsum and rock salt, indicating favorable prospects for exploration and development. Previous investigations of rock salt deposits in this area have primarily relied on drilling and seismic exploration. Although these methods provide high resolution, they are associated with high costs and significant environmental disturbance, which to some extent constrain efficient resource development. To investigate the three-dimensional electrical characteristics of the rock salt deposit, six audio-frequency magnetotelluric (AMT) survey lines were deployed in the study area, and a total of 42 MT stations were acquired. Dimensionality analysis indicates that the subsurface geological structure exhibits pronounced three-dimensional electrical features. Subsequently, a prior-information-constrained three-dimensional inversion was conducted, leading to the establishment of a resistivity structural model characterized by “shallow low resistivity–intermediate high resistivity–deep low resistivity” zoning. Integration with regional geological data suggests that the shallow low-resistivity layer corresponds to Quaternary and Neogene unconsolidated sediments, whereas the deep low-resistivity zone is interpreted as the potential occurrence zone of rock salt deposits. The results demonstrate that three-dimensional AMT exploration provides reliable geophysical evidence for deep mineral prospecting and offers technical support for the scientific evaluation of salt resources and the development of underground gas storage caverns. Full article

Magnetotelluric (MT) inversion models are widely used to interpret crustal conductivity structures related to fluid pathways, deformation zones, and mineralization processes; however, evaluating the reliability of inversion-derived anomalies remains challenging when datasets contain subtle station-dependent distortions or residual cultural noise. We present a jackknife-inspired, model-space diagnostic framework based on leave-one-station-out (LOSO) inversion to quantify station influence and improve interpretation reliability. The workflow consists of (1) generating a LOSO inversion ensemble using identical inversion settings, (2) computing ensemble statistics and standardized perturbation metrics to identify sensitive zones, and (3) applying distribution-based diagnostics to classify station influence and guide construction of an ensemble-refined model. Synthetic experiments demonstrate that the framework distinguishes localized station-controlled artifacts from broadly supported structural responses, allowing targeted correction without altering robust features. Application to a field MT dataset acquired in a noise-affected environment shows that a mid-crustal conductive structure remains stable across the LOSO ensemble, while some shallow anomalies exhibit strong station dependence. The resulting ensemble-refined model introduces only localized modifications, demonstrating that ensemble-based model-space diagnostics provide a practical and reproducible strategy for validating MT inversion results and improving confidence in exploration-oriented conductivity interpretations. Full article

Volcanic magma plumbing systems is essential for understanding crustal–mantle material exchange and the dynamics of volcanic activity. The magnetotelluric method (MT) offers an effective tool for imaging conductive features from the crust to the lithospheric mantle. However, current survey strategies face a tradeoff between imaging resolution and acquisition cost. Here, we construct a lithosphere-scale synthetic model of a magma plumbing system and use 3D MT inversion, sensitivity analysis, and point spread function evaluation to assess the resolving capability of sparse versus dense arrays. Our results show that large-scale conductive anomalies in the mid–lower crust and lithospheric mantle can be reliably imaged using a sparse regional array with targeted densification in the crustal anomaly zone. This approach reduces field costs and computational demand. Guided by these findings, we conducted MT observations across the Longgang volcanic field and identified low-resistivity anomalies extending from the lithospheric mantle into the mid–lower crust. These features are consistent with the dense array MT inversion results. Our study demonstrates that an array strategy combining wide-area sparse coverage with targeted densification offers a cost-effective approach to image deep conductive structures, which may provide practical guidance for optimizing MT survey design in volcanic regions. Full article

To address the technical challenges in exploring concealed high-grade iron deposits in China, this study focuses on Banded Iron Formation, BIF, which represents the largest reserves and hosts the greatest number of large-scale deposits in the country. The Gongchangling iron deposit, a typical high-grade iron deposit in the Anben region, was selected as the main study area. In situ measurements and statistical analysis of the geophysical parameters of rocks and ores were conducted, with an emphasis on evaluating their sensitivity to high-grade magnetite mineralization. Based on this analysis, an integrated gravity, magnetic, and electrical survey method was identified as the optimal exploration approach. Building on this foundation, high-precision gravity and magnetic surveys were performed to investigate the geophysical anomaly response mechanisms of the Gongchangling-type high-grade ores. Forward and inverse modeling were applied to identify deep-seated concealed iron ore bodies, with results further validated by audio-frequency magnetotellurics. This study enhances the methodological framework for mineral exploration, improves prospecting efficiency, and provides practical insights to support new breakthroughs in exploration initiatives. Full article

The Jaboi geothermal field, located on Weh Island in western Indonesia, has a potential output of approximately 55 MWe. Previous geophysical surveys have not sufficiently identified the components of the geothermal system. The success of drilling in identifying a geothermal system depends heavily on the accuracy of the conceptual model. Consequently, developing a more precise subsurface model is crucial to minimizing drilling failures. This study aims to map the resistivity structure of the Jaboi geothermal field using the magnetotelluric method. In our research, we used 16 magnetotelluric sites that recorded data for 7 to 8 h. We successfully estimated the cap rock area with resistivity < 10 Ωm distributed across Jaboi Volcano to depths of 500 m and identified an intense resistive anomaly starting at depths of 1–2 km with resistivity > 5000 Ωm. This anomaly is probably due to a block of crystalline basement being uplifted by upwelling magmatic intrusions. The reservoir zone was estimated to be located directly below the cap rock area. The resistivity structure also reveals a fluid pathway zone in the upflow and outflow zone that connects the reservoir to the surface manifestations influenced by the Ceunohot Fault and Jaboi Fault. The resistivity structure confirmed the boundary of the Jaboi geothermal system along the coastline and in the southeastern part. This study successfully identifies key components of geothermal systems, including cap rock, reservoir zones, and fluid migration pathways. Full article

We propose Res-FormerNet, an improved inversion network that integrates a lightweight Transformer encoder into a ResNet50 backbone to enhance two-dimensional magnetotelluric (MT) inversion. The model is designed to jointly leverage residual convolutional structures for local feature extraction and global attention mechanisms for capturing long-range spatial dependencies in geoelectrical resistivity models. To evaluate the effectiveness of the proposed architecture, more than 100,000 synthetic models generated by a two-dimensional staggered-grid finite-difference forward solver are used to construct training and validation datasets for TE and TM apparent resistivity responses, with realistic noise levels applied to simulate field acquisition conditions. A smoothness-aware loss function is further introduced to improve inversion stability and structural continuity. Results from synthetic tests demonstrate that incorporating the Transformer encoder substantially enhances the recovery of large-scale anomalies, structural boundaries, and resistivity contrasts compared with the original ResNet50. The proposed method also exhibits strong generalization capability when applied to real MT field data from southern Africa, producing inversion results highly consistent with those obtained using the nonlinear conjugate gradient (NLCG) method. These findings confirm that the Res-FormerNet architecture provides an effective and robust framework for MT inversion and illustrate the potential of hybrid convolution–attention networks for advancing data-driven electromagnetic inversion. Full article

In this study, we develop a methodology to quantitatively integrate well resistivity logs and audio-magnetotelluric (AMT) sounding in the context of groundwater investigations. The experiments were conducted in a complex Quaternary depositional environment within a region of intensive groundwater use. A synthetic resistivity model was constructed from well resistivity log data and used for forward modelling to generate synthetic AMT responses, which were then inverted using Occam’s algorithm. The AMT-derived resistivity model was subsequently compared with the model obtained from the inversion of the field AMT sounding using the Pearson correlation coefficient (r) and the root mean square error (RMSE). A scalar shift factor (k) was introduced to optimize the match between both models. The comparison between the AMT-derived resistivity model and the well resistivity logs yielded a Pearson correlation coefficient of 0.669 and an RMSE of 0.1911. The optimal scalar shift factor was k = 1.1854, with a 95% confidence interval of [1.1470, 1.2246], indicating only a minor discrepancy. These results demonstrate that AMT can successfully recover a resistivity structure consistent with well resistivity logs. The proposed quantitative integration and validation workflow provides a robust framework to reduce the inherent ambiguity in AMT interpretation and highlights its potential as a direct hydrogeophysical tool for groundwater studies. Full article

The Central Asian Orogenic Belt (CAOB) represents one of the largest Phanerozoic accretionary orogenic systems globally, with its easternmost segment located in Northeast China. This study integrated broadband magnetotelluric (MT) surveys, geochemical analyses, and high-pressure, high-temperature electrical conductivity experiments to elucidate the deep structural characteristics and tectonic evolution of the Heihe-Hegenshan Suture (HHS) within the CAOB. A dense MT profile survey comprising 15 stations was deployed across the HHS, revealing distinct high-conductivity anomalies interpreted as the suture zone and associated tectonic features. Geochemical and petrophysical analyses of representative andesite and granite samples under simulated crustal conditions (573–973 K, 1.0 GPa) provided critical constraints for MT data interpretation. The integration of MT inversion results with aeromagnetic and Bouguer gravity anomaly data delineates the strike and spatial extent of the HHS, confirming its continuity and northward extension beyond previously recognized limits. Numerical modeling of geothermal gradients and electrical conductivity–depth relationships highlights the dominant role of hydrothermal fluids and alteration minerals in controlling shallow high-conductivity anomalies (<5 km), while deeper structures (>5 km) reflect temperature-controlled rock conductivity. These findings offer novel insights into the lithospheric-scale architecture and geodynamic processes governing the HHS, advancing our understanding of complex accretionary orogenesis in the CAOB. Full article

As a clean and renewable energy source with huge reserves, hot dry rock geothermal resources have received wide attention. The geothermal field plays a crucial role in studying the heat source mechanism of hot dry rock, defining target areas, and evaluating resources. In this study, the three-dimensional structural inversion of the Gonghe Basin is carried out using magnetotelluric sounding, and the Curie isothermal surface is obtained by analyzing regional aeromagnetic data. By coupling low-resistance and high-conductivity zones with temperature distribution and integrating the Curie isothermal surface with high-temperature anomalies of some melts, we constructed an initial temperature field model based on comprehensive geophysical data. The temperature field model of the Gonghe Basin is established by using the adaptive finite-element temperature conduction control equation and the constraints of the temperature data from geothermal wells. The temperature field model provides a basis for the future exploration of hot dry rock resources in the Gonghe area. Full article

This article addresses a two-dimensional inverse problem of magnetotelluric sounding under the assumption of E-polarized electromagnetic fields. The main focus is on the construction of a forward numerical model based on the Helmholtz equation with a complex coefficient, and the recovery of electrical conductivity from boundary measurements. The second-order finite difference method is employed for numerical simulation, providing stable approximations of both the direct and the conjugate problems. The inverse problem is formulated as a minimization of a data misfit functional, and solved using Nesterov’s accelerated gradient descent method, which ensures fast convergence and robustness to noise. Numerical experiments are presented for a synthetic model featuring a smooth background conductivity and a localized anomaly. Comparison between the exact and reconstructed solutions demonstrates the high accuracy and efficiency of the proposed algorithm. The developed approach can serve as a foundation for constructing practical inversion schemes in geophysical exploration problems. Full article

The increasing demand for critical minerals is forcing the mineral exploration industry to search for deposits beneath deeper cover and over larger areas. MobileMT, an airborne passive, broadband, total-field AFMAG-class system, couples three-component measurements of airborne magnetic field variations with a remote electric-field base station to image electrical resistivity from the surface to depths of >1–2 km. We present a workflow that integrates MobileMT data with the parallelized, adaptive finite-element 2.5D open-source inversion code MARE2DEM, accompanied by automated mesh generation procedures, to create a rapid and scalable workflow for deep ore exploration. Using this software on two field trials, we demonstrate that (i) high-frequency (>4 kHz) data are essential for recovering not only shallow geology but also, when combined with low frequencies, for refining deep structures and targets and that (ii) base station effects modify the shape of the apparent conductivity curve but have negligible impact on the inverted sections. The proposed workflow is a reliable and effective approach for identifying mineralization-related features and refining geologic models based on data from extensive airborne geophysical surveys. Full article