Methods For Mineral Exploration Research Articles

Domain Adaptation from Drilling to Geophysical Data for Mineral Exploration

This study utilizes domain adaptation to enhance the integration of diverse geoscience datasets, aiming to improve the identification of ore bodies. Traditional mineral exploration methods often face challenges in merging different geoscience data types, which leads to models that do not perform well across varying domains. Domain adaptation is a deep learning strategy aimed at adapting a model developed in one domain (source) to perform well in a different domain (target). To adapt models trained on detailed, labeled drilling data (source) to interpret broader, unlabeled geophysical data (target), Domain-Adversarial Neural Networks (DANNs) were applied, chosen for their robust performance in scenarios where the target domain does not provide labels. This approach was indirectly validated through the minimal overlap between regions identified as candidate ore and borehole locations marked as host rocks, with qualitative validation provided by t-Distributed Stochastic Neighbor Embedding (t-SNE) visualizations showing improved data integration across domains.

Reducing uncertainty in source area exploration of mineralized glacial erratics using terrestrial cosmogenic radionuclide dating

Mineral exploration often relies on sedimentary indicators as first signs of a potential nearby mineralization in bedrock. The transportation of sediment by glacial and fluvial processes introduces uncertainty into the tracing of potential source areas of the sediment. This is particularly challenging in areas where glacial erosion has been weak, resulting in reworking of sediments and multiple directions of transportation. In this study we explore the use of Terrestrial Cosmogenic Nuclides (TCN) alongside conventional mineral exploration methods to better link indicators with their potential source areas.The study focuses on a mineral exploration project site in northern Finland in a region with stratigraphic evidence of multiple glaciations. The project targets the source of discovered Au mineralized erratic boulders that have been deposited atop the most recent till unit. The superposition suggests transportation in the latest glacial event. However, the 10Be (35.9 ± 1.3 and 30.3 ± 1.1 ka) and 26Al TCN ages analyzed from the mineralized erratics precede the latest glacial event, suggesting the possibility of multiple stages of transportation. The local bedrock TCN inventories (48.9 ± 1.9 and 85.3 ± 2.8 ka) are well preserved, suggestive of weak glacial erosion and therefore short recent transportation distances for the mineralized erratics. By combining the TCN interpretation and historical ice flow directions derived from the till stratigraphy, we suggest a nearby source locating NNW of the dated erratics.We find that TCN dating can limit some of the transportation related uncertainties in glaciated terrain. Through the analysis of TCN inventories from bedrock and boulders it is possible to characterize glacial erosion and boulder transportation, and to identify repeated exposure events, i.e., the possibility of multi-staged transportation. The method benefits from combined use of stratigraphic investigations that can identify both the local transportation directions and local glacial coverage history. TCN sampling has a minimal environmental impact, can be used in remote areas and can provide information about the transport history already in the early stages of exploration. Although the analysis is time consuming, the survey is light to conduct and informative even with a small number of samples.

A performance study of local outlier detection methods for mineral exploration with geochemical compositional data

In exploration geochemistry, mineral deposits are typically characterised by an enrichment of the targeted elements, and thus their element composition differs from that of samples in a local neighbourhood. Local outlier detection methods aim at identifying local changes. In contrast to conventional outlier detection procedures, local outlier detection methods are multivariate methods for outlier identification that incorporate the spatial neighbourhood of the samples. It is essential that geochemical data are treated as compositional data, and the requirements for their treatment depend on the specific local outlier detection method. We demonstrate how prominent local outlier detection methods can be used for mineral exploration with geochemical data that vary in scale, in the sampling density, and in data quality. The methods are compared based on known mineralisations, and recommendations for their usefulness are provided.

A surface-tunnel frequency domain electromagnetic method for mineral exploration in Tajikistan area

For old mines, numerous mining tunnels exist, which can potentially bring us closer to the deep ore-bearing structures. Therefore, we propose a surface-tunnel frequency domain electromagnetic (EM) method to utilize these mining tunnels for geophysical exploration. In this method, the transmitter is placed on the Earth’s surface, while the receiver is positioned within the tunnel space, providing higher resolution due to its proximity to the target body. This paper presents the derived analytical solution for the electric field in the surface-tunnel configuration. We also propose a survey system for our surface-tunnel frequency domain electromagnetic method and provide a field example of lead-zinc deposits in Tajikistan. Synthetic cases demonstrate a significant enhancement of the EM signal when the receiver is moved into the tunnel. The field application validates the practicality of our surface-tunnel frequency domain EM method for deep mineral exploration in active mines.

Integrating earthquake-based passive seismic methods in mineral exploration: Case study from the Gerolekas bauxite mining area, Greece

As the global need for aluminum constantly rises, bauxite is considered to be a critical mineral, and the mining industry is in search of new and effective exploration solutions. In this context, we design and implement a purely earthquake-based passive seismic survey at the Gerolekas bauxite mining site in Greece. It is a very difficult exploration setting, characterized by rough topography, limited accessibility, and a very complex geotectonic regime. We gather a passive seismic data set consisting of four months of continuous recordings (May to August 2018) from 129 stand-alone 3C seismological stations. We then analyze this data set and extract 848 microearthquakes that will serve as sources for the application of local earthquake tomography (LET) and transient-source seismic interferometry (TSI) by autocorrelation. We apply LET to estimate the 3D P- and S-wave velocity models of the subsurface below the study area and TSI by autocorrelation to retrieve the zero-offset virtual reflection responses below each of the recording stations. The velocity models provide a relatively coarse image of a previously completely unexplored part of the mining concession, whereas the higher-resolution virtual reflection imaging illuminates in detail the different interfaces. We also reprocess three lines of legacy active seismic data that were shot in 2003, using the LET P-wave velocity model for depth migration, and confirm the improvement of seismic imaging. Finally, we evaluate the obtained results using well data and jointly interpret them, extracting useful information on the expected target depths and indicating that earthquake-based passive seismic techniques can be an innovative and environmentally friendly option for mineral exploration.

Fuzzy-logic technique for gold mineralization prospecting using Landsat 9 OLI processing and fieldwork data in the Bibemi goldfield, north Cameroon

Identifying potential hydrothermal alteration areas is indeed an essential method for mineral exploration. In this research, we developed an algorithm for the delineation of alteration mineral deposits related to gold mineralization in the Bibemi region using set of criteria derived from Landsat 9 OLI data using false colour composites, band ratios, principal component analysis, spectral angle mapper, and fuzzy-logic overlay methods. The methods used showed iron-oxides, ferrous, and hydroxyl-bearing and carbonate mineral properties related to gold mineralization. The fuzzy overlay map identified regions depending on their mineralization prospective, serving as foundation for prospective mineral deposit evaluation investigation, which was produced by the merging of band ratios and PC's alteration markers labelled very good, and excellent and encompasses 0.8–0.9, 0.9–1.0 respectively. The identified regions fit gold mineralization zones based on their potential as proven by prior and field research. In addition, lineaments analysis showed the presence of three main structural direction impacting the Bibemi region (N–S, NNE-SSW, and ESE-WNW to SSE-NNW), when merged with identified rock formations permits the possible deposition of mineral deposits. The innovative aspect of this research is the integration and processing of Landsat 9 OLI and fieldwork data, which allows for the identification of potentially mineralized rock formations and defining exploration targets.

Review of till geochemistry and indicator mineral methods for mineral exploration in glaciated terrain

Since the 1970s, till geochemical and indicator mineral methods for mineral exploration, provenance studies and environmental research in glaciated terrain have been developed, tested and refined. This review summarizes these methods, focusing on field and laboratory methods for till geochemical, indicator mineral and boulder surveys. This review of protocols is intended as a guide for the mineral exploration industry and publicly funded agencies. It summarizes till as a sample medium, and describes the formation of glacial dispersal trains, along with methods for till sample collection, sample processing, matrix geochemistry, indicator mineral analyses, quality assurance/quality control procedures and data reporting and interpretation. The methods described here can be used to conduct reconnaissance- to deposit-scale till sampling surveys to assess mineral resource potential and establish environmental baselines. Supplementary material: Appendix A – Photographs of till types described in text; Appendix B – Logistical and geological factors to consider in till sample survey design; Appendix C – Photographs of glaciate terrain types described in text; and Appendix D – Till sample processing and analysis flow charts are available at https://doi.org/10.6084/m9.figshare.c.6786087 Thematic collection: This article is part of the Reviews in Exploration Geochemistry collection available at: https://www.lyellcollection.org/topic/collections/reviews-in-exploration-geochemistry

Integration of Electrical Resistivity Tomography and Induced Polarization for Characterization and Mapping of (Pb-Zn-Ag) Sulfide Deposits

The accurate characterization and mapping of low-grade ore deposits necessitate the utilization of a robust exploration technique. Induced polarization (IP) tomography is a powerful geophysical method for mineral exploration. An integrated survey using electrical resistivity tomography (ERT) and IP was employed in this study to characterize and map (Zn-Pb-Ag) ore deposits in NE New Brunswick, Canada. The survey encompassed twelve parallel lines across the study area. The 2D and 3D inversion of the results provided a detailed image of the resistivity and chargeability ranges of subsurface formations. The boundaries of sulfide mineralization were determined based on resistivity values of (700–2000 Ohm.m) and chargeability values of (3.5 mV/V) and were found to be located at an approximate depth of 80–150 m from the surface. The findings were validated through a comparison with data from borehole logs and mineralogy data analysis. The size and shape of sulfide deposits were successfully characterized and mapped in the study area using this cost-effective mapping approach.

Seismic Imaging of Mineral Exploration Targets: Evaluation of Ray- vs. Wave-Equation-Based Pre-Stack Depth Migrations for Crooked 2D Profiles

Seismic imaging is now a well-established method in mineral exploration with many successful case studies. Seismic data are usually imaged in the time domain (post-stack or pre-stack time migration), but recently pre-stack depth imaging has shown clear advantages for irregular/sparse acquisitions and very complex targets. Here, we evaluate the effectiveness of both ray-based and wave-equation-based pre-stack depth imaging methodologies applied to crooked-line 2D seismic reflection profiles. Seismic data were acquired in the Kylylahti mining area in eastern Finland over severely folded, faulted and subvertical Kylylahti structure, and associated mineralization. We performed 3D ray-based imaging, i.e., industry-standard Kirchhoff migration and its improved version (coherency migration, CM), and wave-equation-based migration, i.e., reverse time migration (RTM) using a velocity model built from first-arrival traveltime tomography. Upon comparing the three different migrations against available geological data and models, it appeared that CM provided the least noisy and well-focused image, but failed to image the internal reflectivity of the Kylylahti formation. RTM was the only method that produced geologically plausible reflections inside the Kylylahti formation including a direct image of the previously known shallow massive sulfide mineralization.

Microscopic Morphology and Indicative Significance of Nanoscale Au Particles in Soils and Fault Muds: A Case Study of Jiaojia, Shandong Province

In recent decades, the human demand for mineral resources has increased dramatically, and the mining of shallow deposits has basically been completed. The prospecting direction has turned to concealed deposits. For this reason, various penetrating geochemical methods have been developed to find concealed minerals and a series of geochemical exploration techniques have been proposed. At the same time, the use of the geochemical gene as a new technique presented in recent years is feasible in discussing component classification and provenance tracing. In this study, we applied these methods for mineral exploration in the Jiaojia gold deposit in Shandong Province, China. The results show that a large number of ore-forming element particles can be observed in ores, fault muds, and soils; compared with Chinese soil, Au has higher enrichment coefficients; according to the LG03 lithogene, the ores belong to a neutral composition, and the fault muds and soils belong to an acidic composition. Based on the above results, it can be found that the ore-forming elements in the Jiaojia gold deposit have migrated. Although this migration cannot change the original lithology, it can provide theoretical support for the fine-grained soil-prospecting method.

SQUIDs for magnetic and electromagnetic methods in mineral exploration

Research on quantum sensors for the detection of magnetic fields (quantum magnetometers) is one of the fast-moving areas of Quantum Technologies. Since there exist expectations about their use in geophysics, this work will provide a brief overview on the various developing quantum technologies and their individual state of the art for implementing quantum magnetometers. As one example, the developments on superconducting quantum interference devices, so-called SQUIDs as a specific implementation of a quantum magnetometer, are presented. In the course of this, SQUID instrument implementations and associated demonstrations and case studies will be presented. An airborne vector magnetometer with ultra-low noise (<10 mathrm{fT}/sqrt{mathrm{Hz}}) and high dynamic range of >32 mathrm{bit} will be introduced which has the prospect to be applied for the magnetic method in parallel with electromagnetic methods such as passive audio-frequency magnetics or semi-airborne methods using active transmitters such as elongated grounded dipole sources. The according signals are separated in the frequency domain. A second implementation is an airborne full tensor gradiometer instrument will be discussed which has shown already a number of successful case studies and which turned into commercial operation in the past years. Besides the airborne instrument, a very successful implementation of quantum magnetometers is the SQUID-based receiver for the ground-based transient electromagnetic method. Today it is a mature technology which has been in commercial use for more than a decade and has led to a number of discoveries of conductive ore bodies. One case study will be presented which demonstrates the performance of this instrument. Finally, future prospects of using quantum magnetometers, including SQUIDs and new optically pumped magnetometers, in geophysical exploration will be discussed. Particular applications for both sensor types will be introduced.

Cost‐effective in‐mine seismic experiments to image platinum deposits and associated geological structures at Maseve platinum mine, South Africa

ABSTRACTThe detection of mineral deposits and their related geological structures is of great importance to the mining industry as structures (such as dykes and faults) can affect the safety, cost and efficiency of mining. With the goal of testing cost‐effective seismic methods for mineral exploration and mining, active and passive seismic experiments were conducted at Maseve platinum mine in the Bushveld Complex (South Africa) in 2020. The experiments involved surface‐passive (using 5 Hz wireless nodes; single vertical component) and in‐mine active reflection seismic surveys (using 4.5 Hz land streamer and 5 kg sledgehammer) to image geological structures and delineate economic platinum‐group elements bearing Merensky and Upper Group‐2 chromitite layers (known as reefs). This paper presents only the results from the in‐mine active seismic experiments. The in‐mine seismic surveys consisted of seven 2D reflection seismic profiles in the development tunnels, which were located ∼550 m below ground surface and a few tens of metres above known mineralizations: the Upper Group‐2 and Merensky Reef. The data were carefully processed to enhance the reflections and suppress noise generated by mine infrastructure (e.g., equipment and ventilation). We successfully imaged the Merensky Reef and Upper Group‐2 orebodies approximately 55 m and 124 m below the tunnel floor, respectively, and delineated faults and dykes that crosscut them. Furthermore, the seismic data reveal relatively strong amplitude and faulted reflections below the Upper Group‐2 that may represent deeper chromitite‐enriched orebodies. However, the economic value of these horizons can only be confirmed through drilling. The processed seismic data were combined with borehole data, synthetic modelling and geological models to constrain the interpretation. This study encourages the use of in‐mine seismics for future mineral exploration, mine development and planning.

Application of the fine-grained soil prospecting method in a loess-covered area of central China

Loess-covered landscapes occupy a large area of the globe and have substantially high potential for mineral exploration; however, as mineral information is obscured by loess cover, suitable prospecting techniques need to be applied. The fine-grained soil prospecting method—a deep-penetrating geochemical technology that can be used to identify concealed deposits—has been proven effective in some cases. In this study, we applied this method for mineral exploration in the loess-covered Luoning Basin in Central China. Our results revealed strong geochemical anomalies (e.g., Au, Ag, Pb, Zn, and Cu) over related and concealed ore deposits. Furthermore, a regional geochemical survey in the Luoning Basin revealed the spatial distribution and suites of elements that were consistent with the mineralization type. Moreover, higher geochemical anomalies of Au, Ag, Pb, and Zn were spatially related to an Au ore deposit and Ag–Pb–Zn polymetallic deposit, respectively. The results of a detailed geochemical survey in the Zhonghedi Ag–Pb–Zn polymetallic deposit further revealed that the distribution of surface element anomalies was associated with tectonic fractures throughout the exploration region, which are closely related to the distribution of orebodies. These results imply that the fine-grained soil prospecting method is suitable for anomaly delineation during detailed geochemical surveys as well as regional-scale surveys. Based on our results, we suggest that geochemical anomalies in the loess-covered surface in our study area are presumably the result of geogas dispersion processes; we provide a schematic model explaining how ore-forming and associated materials are brought to the surface by geogas flowing upwards along faults and fractures and, ultimately, accumulating in fine-grained loess soils. Overall, our research demonstrates that fine-grained soil prospecting can effectively aid the search for concealed mineral deposits in loess-covered landscapes.

DCA Method in Mineral Exploration, Example: Predict the Location of New Samples

As the name implies, Discriminant Correspondence Analysis (DCA) is a format of Discriminant analysis (DA) and correspondence analysis (CA). Like differential analysis, the goal is to categorize observations into predefined groups and, like Correspondence analysis, to use nominal variables. The main idea of the DCA is to represent each set of observations and perform a simple Correspondence analysis on the variables (a matrix). The main observations are complementary elements, and each observation is attributed to the closest group. A comparison between the predictions and predictions of classification leads to evaluating the Discriminant correspondence. This information can be used for a similar case to classify new observations, and the validation of estimates can also be examined using cross-validation techniques such as Jack Knife or Bootstrap. For example, samples were taken from different regions. After scoring the parameters and training in this analysis, a new sample was entered, and a group (region) was determined compared to the previous samples.

3-D Inversion of Gravity Anomalies by Combining Power-Spectrum Derived Adaptive Weighting and Cross-Gradient Regulation: Application to Molybdenum–Copper Deposit

Gravity measurement is an important geophysical prospecting method for mineral exploration. With most of the shallow ore deposits in China being exploited, the future targets for exploration will be aimed at the deep mineral resources about 4-km underground. To improve the resolving ability in the vertical direction of the 3-D density inversion to find deep-source minerals, we propose to achieve the inversion of gravity anomalies by combining power-spectrum derived adaptive weighting and cross-gradient regularization. First, spectral analysis is utilized to conduct the source-depth separation, and the adaptive weighting function is designed depending on the slope of the radial logarithmic power spectrum of the gravity anomaly, which can enhance the correspondence for the field sources with different depths to improve the vertical resolution relatively. Thus, each separated source with different depths could be given an adaptive weighting coefficient in each separated inversion. Second, the cross-gradient technique is introduced as a structural constraint in the objective function to further constrain the separated inversion process. By performing two-cuboid-source cases, it can be seen that this combination calculated approach has great potential to improve the quality of the inversion results. When examining the inversion of the actual gravity data from certain ore district in the west of Zhen’an, South Qinling, we speculate that a potential deep ore body would exist in the deposit via utilizing the recovered density model obtained by the proposed method.

Application of Pseudo-random electrical exploration method in mineral exploration: a case study of skarn-type ore body

Skarn-type ore body containing rich mineral resources, which is a type of deposit with important industrial significance and a wide distribution, is formed by metasomatism of mineral gas-bearing hydrothermal fluids on or near the contact zone between intermediate-acid-medium-basic intrusive rocks and carbonate rocks. It is hard to obtain stable data by using conventional electrical prospecting method because of strong electromagnetic interference. A new pseudo-random method is used to do geological survey work in Northeast China for interference avoidance.

Exploring the Potential of HySpex Hyperspectral Imagery for Extraction of Copper Content.

Detritus geochemical information has been proven through research to be an effective prospecting method in mineral exploration. However, the traditional detritus metal content monitoring methods based on field sampling and laboratory chemical analysis are time-consuming and may not meet the requirements of large-scale metal content monitoring. In this study, we obtained 95 detritus samples and seven HySpex hyperspectral imagery scenes with a spatial resolution of 1 m from Karatag Gobi area, Xinjiang, China, and used partial least squares and wavebands selection methods to explore the usefulness of super-low-altitude HySpex hyperspectral images in estimating detritus feasibility and effectiveness of Cu element content. The results show that: (1) among all the inversion models of transformed spectra, power-logarithm transformation spectrum was the optimal prediction model (coefficient of determination(R2) = 0.586, mean absolute error(MAE) = 21.405); (2) compared to the genetic algorithm (GA) and continuous projection algorithm (SPA), the competitive weighted resampling algorithm (CARS) was the optimal feature band-screening method. The R2 of the inversion model was constructed based on the characteristic bands selected by CARS reaching 0.734, which was higher than that of GA (0.519) and SPA (0.691), and the MAE (19.926) was the lowest. Only 20 bands were used in the model construction, which is lower than that of GA (105) and SPA (42); (3) The power-logarithm transforms, and CARS combined with the model of HySpex hyperspectral images and the Cu content distribution in the study area were obtained, consistent with the actual survey results on the ground. Our results prove that the method incorporating the HySpex hyperspectral data to invert copper content in detritus is feasible and effective, and provides data and a reference method for obtaining geochemical element distribution in a large area and for reducing key areas of geological exploration in the future.

3DWofE: An open-source software package for three-dimensional weights of evidence modeling

Abstract The shortage of outcropping ore deposits and the inefficiency of traditional mineral exploration methods for discovering deep-seated deposits have increased the necessity of developing three-dimensional modeling methods for in-depth exploration. The 3DWofE is a Python-based open-source software package that provides the tools required for three-dimensional modeling of concealed ore bodies by developing a data-driven prospectivity modeling method called weights of evidence. This software enables users to create three types of models which include posterior probability, uncertainty, and studentized posterior probability. These models can guide exploration geologists through identifying potential regions of target mineralization in depth.

The Efficient 3D Gravity Focusing Density Inversion Based on Preconditioned JFNK Method under Undulating Terrain: A Case Study from Huayangchuan, Shaanxi Province, China

Since polymetallic ores show higher anomalies in gravity exploration methods, we usually obtain the position and range of ore bodies by density inversion of gravity data. The three-dimensional (3D) gravity focusing density inversion is a common interpretation method in mineral exploration, which can directly and quantitatively obtain the density distribution of subsurface targets. However, in actual cases, it is computation inefficient. We proposed the preconditioned Jacobian-free Newton-Krylov (JFNK) method to accomplish the focusing inversion. The JFNK method is an efficient algorithm in solving large sparse systems of nonlinear equations, and we further accelerate the inversion process by the preconditioned technique. In the actual area, the gravity anomalies are distributed on the naturally undulating surface. Nowadays, the gravity inversion under undulating terrain was mainly achieved by discretizing the ground into unstructured meshes, but it is complicated and time-consuming. To improve the practicality, we presented an equivalent-dimensional method that incorporates unstructured meshes with structured meshes in gravity inversion, and the horizontal size is determined by the gradient of observed gravity and terrain data. The small size meshes are adopted at the position where the terrain or gravity gradient is large. We used synthetic data with undulating-terrain to test our new method. The results indicated that the recovered model obtained by this method was similar to the inversion method of unstructured meshes, and the new method computes faster. We also applied the method to field data in Huayangchuan, Shaanxi Province. The survey area has complicated terrain conditions and contains multiple polymetallic ores. Based on the high-density characteristics of polymetallic ore bodies in the area, we calculate the field data into 3D density models of the subsurface by the preconditioned JFNK method and infer six polymetallic ores.

Integration of remote sensing, gravity and geochemical data for exploration of Cu-mineralization in Alwar basin, Rajasthan, India

In spite of the dominance of traditional mineral exploration methods that demand physical characterization of rocks and intense field work, remote sensing technologies have also evolved in the recent past to facilitate mineral exploration. In the present study, we have processed visible near infrared (VNIR) and shortwave infrared (SWIR) bands of Advanced space-borne thermal emission and reflection radiometer (ASTER) data to detect surface mineralization signatures in Mundiyawas - Khera area in Alwar basin, north-eastern Rajasthan, India using spectral angle mapper (SAM). The potential of SAM method to detect target under variable illumination condition was used to delineate galena, chalcopyrite, malachite etc. as surface signatures of mineralization. It was ensured that the identified surface anomalies were spectrally pure using pixel purity index. Spectral anomalies were validated in the field and also using X-Ray diffraction data. Spectral anomaly maps thus derived were integrated using weight of evidence method with the lineament density, geochemical anomaly, bouger anomaly maps to identify few additional potential areas of mineralization. This study thus establishes the importance of remote sensing in mineral exploration to zero in on potentially ore rich but unexplored zones.