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Overview: A glimpse of the latest advances in artificial intelligence and big data geoscience research ZHOU Yongzhang, XIAO Fan Earth Science Frontiers    2024, 31 (4): 1-6.   DOI: 10.13745/j.esf.sf.2024.6.99 Abstract （1202）   HTML （41）    PDF（pc） （640KB）（351）       Knowledge map    Save This special issue titled “Artificial Intelligence and Big Data Geoscience” consists of 17 papers covering topics such as knowledge graphs, deep learning-based image recognition, machine-readable expression of unstructured geological information, big graph data and community detection, association rule algorithms, 3D geological simulation and mineral prospecting, and the Internet of Things and online monitoring systems. A progressive multi-granularity training deep learning method is proposed for mineral image identification; the model achieves 86.5% accuracy on a commonly used dataset comprising 36 mineral types, increasing the accuracy of mineral identification. Knowledge related to porphyry copper ore in the Qinzhou-Hangzhou mineralization belt, South China, is collected using both primary and literature data sources, and Natural Language Processing (NLP) techniques are used to semantically correlate and reason over the knowledge graph, enabling automated knowledge extraction and reasoning. The association rule algorithm is used to analyze the correlation between trace elements and gold mineralization in major Carlin-type gold deposits in the “Golden Triangle” region of Yunnan-Guizhou-Guangxi provinces, China, and combined with the migration and enrichment law of elements to analyze the genetic mechanism of deposits. By builing a quantitative prospecting indicator method based on association rule algorithm, this study provides new ideas for establishing quantitative prospecting indicators for other types of deposits. In study of machine-readable expression of unstructured geological information and intelligent prediction of mineralization associated anomaly areas in Pangxidong District, western Guangdong, China, unstructured geological information such as stratigraphy, lithology and faults is processed by machine-readable conversion, and two machine learning algorithms—namely, One-Class Support Vector Machine and Auto-Encoder network—are applied to mine the geochemical test data of the stream sediment as well as the comprehensive geological information such as faults and stratigraphy, to extract the features of the mineralizing anomalies, and ultimately realize the intelligent circling of mineralizing anomalous areas. In study of networked monitoring of urban soil pollutants and visualized system based on microservice architecture, a system capable of real-time online monitoring, processing, and analyzing urban soil pollution data to enhance the timeliness of predictions and warnings is developed, where the integrated monitoring and data visualization system is based on the microservices framework Spring Cloud Alibaba. The above mentioned studies provide highly valuable application scenarios and research cases, reflecting to some extent the latest research advances in the field of artificial intelligence and big data geoscience in China, and are worthy of peer attention. Reference | Related Articles | Metrics | Comments（0）

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Knowledge graph-infused quantitative mineral resource forecasting WANG Chengbin, WANG Mingguo, WANG Bo, CHEN Jianguo, MA Xiaogang, JIANG Shu Earth Science Frontiers    2024, 31 (4): 26-36.   DOI: 10.13745/j.esf.sf.2024.5.3 Abstract （1085）   HTML （19）    PDF（pc） （6062KB）（233）       Knowledge map    Save Big data and artificial intelligence have greatly transformed mineral exploration practices with the development of innovative mineral forecasting models and improvement of forecasting efficiency for strategic minerals. In the field of quantitative mineral forecasting, comprehensive intelligent forecasting by combining knowledge and data has gradually become a common consensus, however, the challenge lies in how to combine knowledge and data. Knowledge graphs integrate multi-source, heterogeneous geoscience big data and drive knowledge discovery through rules and reasoning. Here, we discuss the feasibility and technical roadmap of knowledge graph-infused intelligent and automated mineral resource forecasting, particularly in consideration of the characteristics of knowledge graphs in the era of big data and artificial intelligence. We focus mainly on the construction of multi-temporal, all-element knowledge graphs for mineral deposit-mineral exploration systems and the methodology for establishing forecasting models from the perspectives of ore commonality and distinctiveness based on knowledge graphs. The opportunities and challenges of knowledge graph embedding for geological anomaly information extraction and quantitative resource forecasting are also discussed, in the hope that the infusion of knowledge representation and reasoning from knowledge graphs into the technical workflow of quantitative mineral resource forecasting can aid geologists in building ore forecasting models and enhancing automated and intelligent mineral forecasting. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Tectonic fracturing and fracture initiation in shale reservoirs—research progress and outlooks DING Wenlong, WANG Yao, ZHANG Ziyou, LIU Tianshun, CHENG Xiaoyun, GOU Tong, WANG Shenghui, LIU Tingfeng Earth Science Frontiers    2024, 31 (5): 1-16.   DOI: 10.13745/j.esf.sf.2024.6.11 Abstract （1068）   HTML （32）    PDF（pc） （7879KB）（202）       Knowledge map    Save Shale oil and gas development has gained significant progress in China with the contineous research and technological advancements in unconventional oil and gas. Extensive production practices demonstrate that natural fracture development in shale reservoirs is a crucial factor influencing oil and gas enrichment, high production and stable yield, for fractures not only improve reservoir properties but also facilitate subsequent reservoir modification during hydrollic fracturing. The formation stages of tectonic fractures and fracture initiation holds significant importance for revealing the oil and gas enrichment patterns and preservation condition. Early studies on shale reservoir fractures mainly focused on fracture classification/identification/characterization, main controlling factors of fracture development, and fracture distribution prediction and modelling, with less attention to the determination of fracture formation stages, main controlling factors of fracture initiation, mechanism of fracture opening and closing, and quantitative characterization of fracture openness—this restricts the efficient exploration and development of shale oil and gas in China. This paper highlights research progress addressing the above gaps, particularly the delineation of fracturing stages, dating of filling veins, and quantification of fracture openness based on comprehensive literature review. The classification methods for fracturing stages can be divided into two categories: qualitative geological analysis and geochemical tracing of fracture fillings. These methods however have practical limitations, where only the relative sequence of fracturing stages can be obtained, and the results are affected by the accuracy of basic geological data such as burial/thermal histories. Most of the fissure veins in fractures are carbonate minerals and quartz. With the advent of high precision in situ U-Pb microprobe dating technology, it is possible to determine the absolute ages of different veins while avoiding the problem of multiple solutions to fluid activity periods due to differences in interpreting thermal/burial histories. The initiation of tectonic fractures is controlled by many factors, not only by rocks’ intrinsic properties but also the current crustal stress and formation-fluid pressure. The petrological characteristics of fibrous fillings widely distributed in fractures record the crystal growth process. Such special crystal morphology provides the evidence of multi-stage tectonic fracturing, revealing a fracture evolutionary process with multiple fracture opening and closing. At present, fracture openness is characterized using the fracture apature parameter or inferred by the fracture initiation pressure obtained by calculation and experiment. Based on the analysis of the above results, this paper points out the key problems and development trends in the study of the fracturing stages and initiation of tectonic fractures in shale reservoirs, aiming to enrich and improve the theory and research methodology for shale oil and gas reservoirs, and provide an important scientific basis for the study of structural preservation conditions and enrichment mechanism of shale oil and gas in China. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Key issues in three-dimensional predictive modeling of mineral prospectivity YUAN Feng, LI Xiaohui, TIAN Weidong, ZHOU Guanqun, WANG Jinju, GE Can, GUO Xianzheng, ZHENG Chaojie Earth Science Frontiers    2024, 31 (4): 119-128.   DOI: 10.13745/j.esf.sf.2024.5.9 Abstract （1005）   HTML （15）    PDF（pc） （3871KB）（390）       Knowledge map    Save Three-dimensional predictive modeling of mineral prospectivity is an important approach to deep mineral exploration. Although significant advancements have been made in the methodology and application of this approach, several key scientific and technological issues remain unresolved concerning the insufficiencies of multi-scale 3D predictive modeling methodology, uncertainty analysis and optimization of prediction results, mining of key factors in 3D mineralization prediction, and dedicated 3D deep learning models and methodologies tailored for 3D predictive modeling of mineral prospectivity. Focusing on these key issues, this paper conducts a comprehensive review of current research progress in the field, and proposes potential solutions and research directions to address these issues. Future developments in this field include methods for deep mining of 3D predictive information; applicable 3D deep learning models and training methods for enhanced predictive modeling; uncertainty analysis and optimization methods for improving the reliability and accuracy of 3D mineralization prediction; and a methodological framework for multi-scale predictive modeling so as to effectively guide deep mineral exploration at the levels of orebodies, ore fields, and ore deposits. Resolving these key issues will further develop and refine the theoretical and methodological frameworks of 3D mineralization prediction, significantly improve the efficiency of deep mineral exploration, and ultimately facilitate breakthrough in mineral deposit discovery in the deep earth. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Characterization and 3D modeling of multiscale natural fractures in shale gas reservoir: A case study in the Pingqiao structural belt, Sichuan Basin QIAO Hui, ZHANG Yonggui, NIE Haikuan, PENG Yongmin, ZHANG Ke, SU Haikun Earth Science Frontiers    2024, 31 (5): 89-102.   DOI: 10.13745/j.esf.sf.2023.6.13 Abstract （1002）   HTML （3）    PDF（pc） （10680KB）（89）       Knowledge map    Save Natural fractures in shale reservoirs are important reservoir spaces and seepage channels. Identifying the types and spatial distribution of natural fractures is essential for shale gas exploration and development. This paper, based on seismic/outcrop data, core observation, well logging and micro-test analysis, mainly considering the effect of fractures on shale gas enrichment and high production, divides natural fractures of shale reservoirs into three scale levels: large, medium-small and micro, and clarifies the methodologies for fracture characterization and modeling at each scale level and application results. In summary: (1) large fractures were mainly characterized using stacked 3D seismic data; medium-small fractures using a combination of core, image log and seismic attributes data; and microfractures using microanalysis such as core description, high-resolution scanning electron microscope and maps analysis. Through fracture characterization, the fracture density, crack opening, dip, orientation and filling status at each scale level were determined. (2) The DFN model of large fractures was established via deterministic modeling, using the characterization parameters of post-stack seismic attributes as the input. For medium-small fractures, single-well image logs were used as prior information; a fracture probability model of multi-information fusion was established as the spatial trend; and the DFN model was established via stochastic modelling. Microfracture modeling was based on microfracture parameters obtained from micro-test analysis; microfracture density model was established by combining well data with TOC and other main control factors; and the DFN model was established via stochastic modeling. (3) Taking the shale gas reservoir in the Pingqiao tectonic zone, Sichuan Basin as an example, fracture characterization and fracture 3D geological modeling for different fracture types were carried out. The fracture initiation site, scale, orientation and occurrence characteristics were defined, and fracture attributes such as fracture location, dip angle, azimuth angle, geometric size, development density, porosity and permeability were described. The methodologies for the multiscale natural fracture characterization and modeling provide a basis for numerical modeling of shale gas reservoirs. The 3D geological model of shale reservoir in the Pingqiao tectonic belt and the simulation results are in good agreement with geological knowledge and production data, thus providing a reference for the devlopment of shale gas fields. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Ocean-floor hydrogen accumulation model and global distribution SUO Yanhui, JIANG Zhaoxia, LI Sanzhong, WU Lixin Earth Science Frontiers    2024, 31 (4): 175-182.   DOI: 10.13745/j.esf.sf.2024.6.98 Abstract （984）   HTML （7）    PDF（pc） （1836KB）（159）       Knowledge map    Save Hydrogen energy is a clean, efficient, and zero-carbon energy source. The formation, transportation, and accumulation of natural hydrogen are closely related to plate tectonics. As the only rocky planet in the solar system known to have plate tectonics and liquid water, Earth has unique geological hydrogen generation pathways such as degassing, serpentinization, and water radiolysis. The ocean-floor, which occupies two-thirds of the Earth’s surface, has great potential for natural hydrogen generation through serpentinization, due to the extensive exposure of oceanic crust or mantle along or around microplate boundaries and ocean-floor fissures. Microplate boundaries, submarine plateaus, ocean floor fracture zones, micro-mantle blocks, and non-volcanic passive continental margins are favorable targets for exploring ocean-floor natural hydrogen. The northeastern continental margin of the South China Sea is also worthy of attention. However, it is difficult to establish a unified ocean-floor hydrogen accumulation model due to the significant differences and diversity in the formation, migration, and storage conditions of natural hydrogen in different tectonic settings. The predicted hydrogen sites, whether they can form reservoirs, how they form reservoirs, and the related exploitation and utilization technologies need to be explored in the future. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Mechanical behavior of calcite vein-bearing shale of the Niutitang Formation in Fenggang area, northern Guizhou based on CT tests WU Zhonghu, MENG Xiangrui, LAN Baofeng, LIU Jingshou, GONG Lei, YANG Yuhan Earth Science Frontiers    2024, 31 (5): 117-129.   DOI: 10.13745/j.esf.sf.2024.6.15 Abstract （958）   HTML （2）    PDF（pc） （10828KB）（86）       Knowledge map    Save Core observations of shales from the Niutitang Formation in the northern Qianbei region show that calcite veins often act as natural fracture fillers and largely influence the shale damage patterns. The damage characteristics of calcite vein-bearing shales is important for the prediction of fracture initiation and extension behavior during hydraulic fracturing and for the engineering design. In order to reveal the influence of calcite veins on the mechanical properties and fracture characteristics of shale, uniaxial compression and acoustic emission tests are conducted at seven inclination angles of 0° to 90° in 15° increment. Combined with CT scanning technology and finite element calculations, a three-dimensional (3D) microscopic numerical model is constructed. The effects of calcite vein angle on the fine-scale shale damage process as well as shale mechanical properties are discussed, and the spatiotemporal evolution of shale microcracks are analyzed. The results show that (1) under different calcite vein angles the shale acoustic emission and stress-strain curves show similar curve shape changes, in four stages, namely compression-density, elasticity, yielding, and post-peak damage, with obvious distinctions between stages. The change curve of the characteristic intensity is “U”-shaped with a local minimum at θ of 75°. (2) Calcite veins significantly affect the damage mode: As the vein angle decreases, the damage mode changes from cleavage to cleavage-type shear, to shear-slip, and finally to cleavage-tension. (3) The reconstructed 3D model is largely consistent with physical testing data, providing insights into the process of crack expansion and penetration at shale’s interior and surface. The spatial distribution of acoustic emission reflects the compression, tension, and shear damage types at different stages, revealing the fracture mechanism of calcite-containing shale from the microscopic point of view. (4) Calcite and matrix simulatineously and anisotropically affect the macroscopic mechanical properties of shale: The higher the calcite vein angle, the stronger its slip guidance effect, and the weaker the mechanical properties of the specimens. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Geochemical characteristics and genesis of lithium rich clay rocks in the Pudi area of northwestern Guizhou ZHANG Qidao, LI Dezong, LI Zhiwei, WANG Donghui, YU Yifan, ZHU Xingqiang, CAI Quanyu, LI Ming Earth Science Frontiers    2024, 31 (4): 258-280.   DOI: 10.13745/j.esf.sf.2023.11.20 Abstract （953）   HTML （15）    PDF（pc） （11592KB）（153）       Knowledge map    Save The Permian Liangshan Formation in the Pudi area of northwest Guizhou Province directly overlays the Cambrian Loushanguan Formation, exhibiting abnormal lithium enrichment in its clay rocks. Studying the enrichment mechanism provides valuable insights for lithium resource development and evaluation in clay rocks, as well as understanding lithium accumulation mechanisms. Various analytical methods including LA-ICP-MS, mapping, AMICS, XRD, SEM, along with U-Pb chronology, are employed to elucidate the elemental geochemistry, provenances, and occurrence states of lithium enrichment in clay rocks. Results reveal lithium-rich clay rocks primarily in the middle and lower sections of the Permian Liangshan Formation, with their occurrence controlled by the karst unconformity surface of the underlying Loushanguan Formation dolomite. Enriched elements such as Li, Ga, V, Nb, Zr, and F are identified, while Ba and Sr are relatively depleted. Light rare earth elements (La, Ce, Nd) predominate, with Y as the main heavy rare earth element. Lithium-rich clay rocks comprise terrestrial deposits with characteristics of terrestrial, transitional, and marine phases, formed in an oxidized environment under a tropical-subtropical warm and humid climate. The zircon age spectrum exhibits five peaks at 2.5 Ga, 1.4 Ga, 980 Ma, 780 Ma, and 530 Ma, with the main peaks at 980 Ma, 780 Ma, and 530 Ma. Lithium in the clay rocks mainly occurs within kaolinite, indicating multiple sources, with impure dolomite of the Cambrian Loushanguan Formation likely being the primary source. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Online monitoring of CO2 using IoT for assessment of leakage risks associated with geological sequestration MA Jianhua, LIU Jinfeng, ZHOU Yongzhang, ZHENG Yijun, LU Kefei, LIN Xingyu, WANG Hanyu, ZHANG Can Earth Science Frontiers    2024, 31 (4): 139-146.   DOI: 10.13745/j.esf.sf.2024.5.15 Abstract （913）   HTML （3）    PDF（pc） （2487KB）（210）       Knowledge map    Save Geological sequestration can be used to reduce CO2 emission without much effect on economic growth. It has become an indispensable technical approach to achieving dual-carbon goals. However, geological sequestration carries significant environmental risks from CO2 leakage at storage sites. To ensure the safety and efficacy of carbon sequestration it is critical that potential leaks can be identified through continuous monitoring. In this regard, the Internet of Things (IoT) is ideal due to its large-scale, continuous monitoring, and intelligent analysis capabilities, yet this technology has not been widely implemented. This paper outlines the basis for sensor selection and sensor node deployment, proposes the design idea for underlying sensor technology, and establishes an IoT CO2 monitoring system for storage sites. Specifically, infrared CO2 sensor is selected as the primary sensor and laser CO2 sensor as the secondary sensor, along with FT-IR patrol monitoring; a combination of real-time optimization of mobile deployment, random deployment, and fixed deployment is used in sensor node deployment; a mix of cluster topology and mesh topology is used in high-risk areas, and star topology and tree topology are used in edge areas connected to the main area. As technology advances, sensor mass production and sensor miniaturization will lead to more efficient and scalable sensor networks, and IoT monitoring technology will play a crucial role in continuous monitoring of carbon storage sites. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Machine-readable expression of unstructured geological information and intelligent prediction of mineralization associated anomaly areas in Pangxidong District, Guangdong, China WANG Kunyi, ZHOU Yongzhang Earth Science Frontiers    2024, 31 (4): 47-57.   DOI: 10.13745/j.esf.sf.2024.5.5 Abstract （904）   HTML （10）    PDF（pc） （6558KB）（197）       Knowledge map    Save The application of big data mining and machine learning algorithms in mineralization prediction has become an important research trend, but unstructured geological data cannot be directly mined—first they need to be converted to machine-readable expressions. In this study of the Pangxidong ore district in western Guangdong Province, the unstructured geological information such as stratigraphy, lithology, faults are converted into machine-readable format, and two machine learning algorithms, namely, One-Class Support Vector Machine and Auto-Encoder Network, are applied to mine the geochemical test data of stream sediments as well as the comprehensive geological information on faults, stratigraphy, etc. to extract the features of mineralization anomalies and ultimately achieve intelligent delineation of the anomaly areas. Through combined application of One-Hot Encoder and the weighted variable method for spatially weighted principal component analysis, the structural transformation of the unstructured geological information is realized, and geological information is maximally preserved for data mining. It is demonstrated that the application of One-Class Support Vector Machine and Auto-Encoder Network can effectively solve the problem of data imbalance, as the numbers of ore and non-ore spots in the study area are seriously unbalanced. The prediction results generated using the integrated, synthesized multi-source geological data are relatively consistent with the observed spatial distribution of Pb-Zn deposits and the actual geological structure in the study area, indicating the two algorithms can effectively identify potential prospecting targets and ore deposits. Compared with traditional geochemical prospecting methods, the intelligent prediction method can process and integrate multi-source geological information about the ore-forming processes and identify mineralization anomaly areas. This method is applicable in prospecting areas without prior ore discovery, thereby improving the efficiency of ore prospecting and increasing the possibility of finding ore deposits. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Characteristics of deep karst fracture-cavity reservoir formation controlled by multi-phase faults matching in the northern Tarim Basin LI Fenglei, LIN Chengyan, REN Lihua, ZHANG Guoyin, GUAN Baozhu Earth Science Frontiers    2024, 31 (4): 219-236.   DOI: 10.13745/j.esf.sf.2023.9.5 Abstract （891）   HTML （9）    PDF（pc） （23578KB）（110）       Knowledge map    Save Investigating the correlation between multi-phase tectonic activity and deep reservoir formation is crucial for oil and gas exploration endeavors. Utilizing seismic data from the Halahatang, Jinyue, and Fuman oilfields, coupled with an analysis of field geological outcrop faults, various seismic fine interpretation methods were employed to delineate faults within the study area. Building upon an understanding of the Middle Cambrian Yuertusi source rock and the characteristics of the Caledonian, Hercynian, and Himalayan accumulation stages, faults controlling oil accumulation were classified into four stages: Early Caledonian, Middle and Late Caledonian, Late Hercynian, and Himalayan. Further analysis of the inheritance relationship, source characteristics, and adjustment effects of multi-stage fractures, along with an assessment of various types of karst fracture-cavity reservoir development, led to discussions on the variations in karst fracture-cavity reservoirs under the influence of strike-slip faults in the study area. Key findings include: (1) Identification of primary factors influencing oil and gas reservoirs, including intra-source faults from the early Caledonian normal fault system facilitating hydrocarbon expulsion from Cambrian source rocks, and outer source faults formed during the late Caledonian enabling communication with source rocks for oil and gas migration and accumulation. Four source rocks-linking models were established based on this understanding. (2) Recognition of three main hydrocarbon generation periods in the study area: late Caledonian, Hercynian, and Himalayan, with inherited development of northwest strike-slip fractures into the Permian during the Late Hercynian period, impacting Garridonian reservoirs, and destruction and adjustment of early oil and gas reservoirs by northeast strike-slip fault systems inherited to the Neogene during the Himalayan period. Three modes of oil and gas remigration were established. (3) Establishment of six types of strike-slip fault control grades based on fracture matching relationships, along with classification of Middle and Late Caledonian strike-slip fault zones in the study area. A mining status map revealed a high matching degree between differential reservoir-controlling faults and oil and gas production. (4) Joint control of reservoirs by strike-slip faults and karstification in the study area, with an established matching relationship between the multi-stage fault system and various types of karst fracture-cavity reservoirs. This understanding has been successfully applied to well location exploration in the study area, yielding favorable results and providing guidance for the exploration and development of karst fracture-cavity reservoirs controlled by strike-slip faults. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Ontology-guided knowledge graph construction for mineral prediction YE Yuxin, LIU Jiawen, ZENG Wanxin, YE Shuisheng Earth Science Frontiers    2024, 31 (4): 16-25.   DOI: 10.13745/j.esf.sf.2024.5.4 Abstract （889）   HTML （9）    PDF（pc） （5732KB）（189）       Knowledge map    Save Knowledge graph construction is an effective means of acquiring and representing knowledge in data-driven research, however, existing knowledge graphs have many problems and limitations in mineral resource prediction. Firstly, relevant studies are few while existing knowledge graphs lack spatiotemporal semantics, which limits the effective representation and analysis of the spatiotemporal characteristics of mineral resources. Secondly, existing graph construction methods emphasize text extraction at the data level, but lack ontology construction involving complex logical relationships and lack effective association between ontology and data layers. As a result, existing knowledge graphs lack in-depth and sufficient semantic information to meet the requirement of mineral resource prediction in expressing complex geoscience concepts and relationships. To address this issue, this study takes an ontology-guided approach to construct a knowledge graph suitable for mineral prediction tasks. We first construct the initial domain ontology on the basis of in-depth understanding of mineral prediction theories and methods; we then integrate the domain ontology with selected mature geological time ontology and geographical space ontology to expand the initial ontology—by embedding spatiotemporal semantics we can effectively express the spatiotemporal characteristics of mineral resources. We also pay attention to the association between ontology and data layers—by establishing rich semantic relationships we can achieve effective inter-node connection and information sharing in the knowledge graph. Experimental results show that the knowledge graph outperformed other existing graphs in terms of knowledge richness and confidence. This study provides a methodology for multi-ontology based knowledge graph construction for mineral prediction, thereby promoting further development of this field. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Pollution Characteristics, Ecological risk and source apportionment of heavy metals in sediments of the Pearl River Basin TU Chunlin, HE Chengzhong, MA Yiqi, YIN Linhu, TAO Lanchu, YANG Minghua Earth Science Frontiers    2024, 31 (3): 410-419.   DOI: 10.13745/j.esf.sf.2023.2.47 Abstract （887）   HTML （13）    PDF（pc） （2813KB）（89）       Knowledge map    Save The enrichment of heavy metals in sediments poses a serious threat to the aquatic environment of the Pearl River Basin. Exploring heavy metal pollution in the sediments of the Pearl River Basin is crucial for preventing and controlling such pollution and for supporting the scientific management of the aquatic environment. Data on the contents of heavy metals (As, Cd, Pb, Cr, Cu, and Zn) in the sediments of the Pearl River Basin published from 2009 to 2022 were collected. Through mathematical statistical analysis, correlation analysis, and positive matrix factorization (PMF) modeling, we discussed the distribution characteristics and pollution sources of heavy metals in the sediments of the Pearl River Basin. We also evaluated the pollution degree and ecological risk of heavy metals based on the geo-accumulation index and potential ecological risk index. The results revealed that the average content of As, Cd, Pb, Cr, Cu, and Zn in the sediments of the Pearl River Basin were 49.29, 2.76, 63.97, 67.44, 48.72, and 186.60 mg·kg-1, respectively. Among them, As, Cd, Pb, and Zn exceeded the average values of stream sediments in southern China, while Cu and Cr were close to the average values of stream sediments in southern China. The pollution of Cd and As in the sediments of the Pearl River Basin is the most serious, with Cd classified as mild to moderate degree and As mainly at a slight degree, while the other four heavy metals showed no pollution. The order of single-factor hazard index of heavy metals in sediments was: Cd>As>Pb>Cu>Zn>Cr, with Cd showing a serious damage level throughout the Pearl River Basin, contributing 70.73% to 93.73% of the ecological risk index. The damage level of As in the Xijiang River, Nanbeipan River, and Pearl River Delta was moderate, while the damage level of other heavy metals such as Pb, Cr, Cu, and Zn was slight. The results of the PMF analysis indicated that the main sources of heavy metals in sediments were the combined pollution sources of mining activities and agricultural activities, coal and industrial activities, atmospheric deposition and traffic pollution sources, and natural sources, with contributions of 21%, 17%, 35%, and 27%, respectively. The first three were all anthropogenic sources, with a cumulative contribution of 73%. Cd and As were mainly derived from mining activities, industrial activities, and agricultural activities. Pb was primarily derived from traffic pollution and mining activities. Cr mainly originated from natural sources, while Cu and Zn were influenced by all four sources. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Fracture formation mechanism in shale oil reservoirs, Qintong Depression, North Jiangsu Basin and its influence on hydrocarbon occurrence GAO Yuqiao, HUA Caixia, CAI Xiao, BAI Luanxi, LU Jia Earth Science Frontiers    2024, 31 (5): 35-45.   DOI: 10.13745/j.esf.sf.2024.6.30 Abstract （875）   HTML （5）    PDF（pc） （9620KB）（92）       Knowledge map    Save The second member of the Funing Formation in Qitong Depression, Subei Basin is a favorable section for shale oil exploration and development, where natural fractures provide important reservoir spaces and seepage channels for shale oil and have an important impact on shale oil exploitation and production increase. Based on core observation, imaging logging, thin section observation and experimental analysis, combined with advanced environmental scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM), this paper investigates into the genetic type, development characteristics, formation mechanism and distribution and occurrence state of natural fractures and their influence on oil and gas occurrence in the study area. The natural fractures are mainly tectonic fractures-including cross-bedding shear fractures, in-bedding shear fractures and in-bedding tensile fractures-and sedimentary rock fractures-mainly bedding fractures with a few sutures. The characteristics of fracture development in the sublayers of the second member vary greatly in the vertical direction. From sublayers Ⅰ to Ⅴ the fracture development intensity decreases and fracture types reduce to a single type; the fracture density is gradually reduced; the fracture extension length is gradually increased; and the fracture filling is gradually weakened. A complex fracture network is formed under various influencing factors including sedimentary rocks, structural setting and abnormal high pressure. The fracture network communicates with the reservoir matrix pores to form a three-dimensional pore-fracture system, providing a good space for shale oil storage and greatly improves reservoir permeability. As SEM/LSCM images show shale oil in the study area occur mainly as free or adsorbed oils in the forms of liquid oil droplets in pores and microfractures or oil films wrapping around mineral particles. The crude oil in fractures is mainly composed of light components, and the pores contain both light and heavy components. The development of natural fractures obviously improves the physical properties of shale reservoir rocks and is conducive to the later fracture network reconstructure—an important guarantee of shale oil enrichment and high-production in the study area. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Fracture pore characteristics and gas accumulation model of marine shales in the northwestern Ordos Basin: A case study of the Ordovician Wulalike Formation CHEN Rubiao, WANG Yuman, HUANG Zhengliang, LI Weiling, YAN Wei, LIANG Feng, GUO Wei Earth Science Frontiers    2024, 31 (5): 46-60.   DOI: 10.13745/j.esf.sf.2023.6.14 Abstract （875）   HTML （7）    PDF（pc） （16069KB）（112）       Knowledge map    Save The Ordovician Wulalike Formation in the northwestern margin of the Ordos Basin is a new prospect for exploring shale gas in the North China plate. Its accumulation conditions and enrichment characteristics are quite different from that of marine shale gas fields in South China. Based on geological data such as drilling cores, logging, laboratory analysis and testing, focusing on the fracture characteristics of the Wulalike Formation, this article explores the accumulation model of marine shale gas in the northwestern margin and obtain four conclusions: (1) The Wulalike Formation, under the control of various sedimentary microfacies, develops siliceous shale, calcareous-siliceous and argillaceous-siliceous mixed shale, localized carbonate rocks (mainly brecciated limestone and marl) and calcareous shale, with large variations in lithofacies combinations in different blocks. However, the lower interval is generally rich in siliceous and exhibits similar brittleness to the lower interval of the Longmaxi Formation, which is beneficial for reservoir fracturing in the foreland thrust belt distribution zone. (2) The Wulalike Formation develops two generations of fractures: high-angle filled fractures and low-angle bedding fractures. Whilst the predominant type is the open bedding microfractures, which is more developed in the southern block compared to the northern block. (3) The lower interval of the Wulalike Formation generally has a total porosity between 2.46%-7.08%, similar to the Longmaxi Formation in the Sichuan basin, with matrix porosity accounting for 34.0%-90.0% (average 61.1%) and fracture porosity 10.0%-66.0% (average 38.9%). (4) Natural gas is mainly stored as free gas (accounting for over 64%), where primary and secondary intralayer migration occurs in inorganic pores and bedding fracture system. According to comprehensive analysis, the Majiatan-Shanghaimiao exploration area is mainly a fractured shale gas accumulation area controlled by structures. The fracture development period is synchronized with the peak gas generation period, which is conducive to the efficient accumulation of natural gas in the Wulalike Formation. The Tiekesumiao Block is a mixed shale gas reservoir. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Metallogenic regularities and exploration directions of strategic metallic minerals around the Qaidam Basin ZHANG Aikui, YUAN Wanming, LIU Guanglian, ZHANG Yong, WANG Zhouxin, SUN Feifei, LIU Zhigang Earth Science Frontiers    2024, 31 (3): 260-283.   DOI: 10.13745/j.esf.sf.2023.2.86 Abstract （871）   HTML （6）    PDF（pc） （3793KB）（138）       Knowledge map    Save Strategic mineral resources play a crucial role in national economic development and security, particularly in regions like the Qaidam Basin where abundant resources are found. Understanding the metallogenic regularity and identifying exploration directions are essential for successful prospecting and ensuring a stable supply of strategic minerals. Based on a comprehensive review of available information in the area, a systematic analysis of the strategic minerals around the Qaidam Basin has been conducted. By examining metallogenic types, characteristics, and integrating geophysical and geochemical data, recommendations for further exploration have been proposed. The key findings are as follows: Gold, nickel, and cobalt are identified as strategic minerals with regional advantages around the Qaidam Basin, with metallogenic periods primarily in the Ordovician, late Silurian-Devonian, and Triassic eras. ① Nickel deposits are syngenetic magmatic deposits associated with mafic-ultramafic rocks, formed in a late Silurian-Devonian post-collision-post-orogenic environment. The presence of well-developed mafic-ultramafic rocks, high MgO content, partial melting degree of primary magma, and specific mineral characteristics favor the formation of significant ore deposits. ② Cobalt deposits exhibit various metallogenic types, including magmatic, sediment-hosted, and hydrothermal types. Magmatic cobalt ore is linked to magmatic copper-nickel-cobalt sulfide deposits related to mafic-ultramafic rocks, with Co grades closely related to Ni content. Sediment-hosted cobalt ores present opportunities in the East Kunlun metallogenic belt. Hydrothermal cobalt deposits comprise exhalative sedimentary and skarn types, with mineralization ages in the Ordovician and Carboniferous periods. ③ Gold mineralization in the region includes orogenic, skarn, porphyry, and epithermal types, with distinct mineralization events occurring between 425.5-401 Ma, 383-349 Ma, 284-263.21 Ma, and 242.2-202.7 Ma. Crust-mantle interactions during the Silurian-Devonian and Middle-Late Triassic periods played a significant role in gold deposit formation. ④ Key mineral deposit exploration targets for the future include magmatic copper-nickel-cobalt sulfide, sedimentary rock-hosted manganese-cobalt, orogenic gold, porphyry copper-molybdenum, lithium-bearing pegmatite, multi-strategic metal composite, and magmatic chromium deposits. Emphasis should be placed on medium-low geomagnetic and geochemical anomaly areas around the Qaidam Basin, with a focus on exploring various deposit types in deep marginal and semi-concealed areas. By considering these findings and recommendations, future mineral exploration efforts in the Qaidam Basin can be strategically planned to maximize the discovery of valuable resources and contribute to national development and security. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Advances and trends on soil methane emission in permafrost region ZHANG Shunyao, SHI Zeming, YANG Zhibin, ZHOU Yalong, ZHANG Fugui, PENG Min Earth Science Frontiers    2024, 31 (4): 354-365.   DOI: 10.13745/j.esf.sf.2023.5.29 Abstract （863）   HTML （7）    PDF（pc） （2635KB）（134）       Knowledge map    Save Soil methane emissions in permafrost regions are integral components of the global carbon cycle and terrestrial ecosystem, playing a pivotal role in the feedback mechanism of carbon sink on climate change, thus warranting focused research in the domain of global climate change. The origins of soil methane emissions in permafrost regions primarily stem from microbial methane production and gas release from frozen soil layers and natural gas hydrates. While research on microbial gas sources is relatively advanced, investigations into methane emissions from frozen soil layers and natural gas hydrate gas sources are still in the qualitative analysis stage. Influential factors such as soil temperature, moisture, water table conditions, organic matter content, surface vegetation conditions, and others can significantly influence various stages of methane production, transport, and oxidation. Modeling stands as the primary approach for evaluating and forecasting soil methane emissions in permafrost regions, encompassing both early statistical models and more recent process models based on the mechanisms of methane emission from soil. Although the synthesis of research on methane emissions from permafrost soils has yielded insights into gas sources and single-factor effects, there remain gaps in the study of multi-source methane emission, particularly concerning methane release from permafrost soil and gas hydrates. Furthermore, the analysis of causal mechanisms and driving forces under multiple factors is lacking in the investigation of influential factors. Comprehensive monitoring research employing diverse methods and factors, such as metagenomic analysis of methane-producing microorganisms and isotope tracing of multi-gas source soil methane emissions, can be integrated with satellite remote sensing and other large-scale observation results to refine process models of methane emissions from permafrost soils. Given that changes in the carbon cycling system of the Qinghai-Tibet Plateau, revered as the “Third Pole” of the world, will exert significant impacts on climate change in Asia and globally, further exploration of soil methane emissions on the Qinghai-Tibet Plateau is imperative to facilitate the quantitative assessment of regional carbon emissions and advance global climate change research. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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InterfaceGrid: Gridding representation of 3D geological models for complex geological structures NIU Lujia, SHI Chengyue, WANG Zhangang, ZHOU Yongzhang Earth Science Frontiers    2024, 31 (4): 129-138.   DOI: 10.13745/j.esf.sf.2024.5.7 Abstract （848）   HTML （9）    PDF（pc） （3722KB）（231）       Knowledge map    Save 3D structural geological models are a digital representation of geological structures and geological body (object) boundaries in geological space. With the increasing demands for raster and vector integration and spatial query and analysis of geological data, the construction of integrated spatial data model for unified expression of geological structures has become one of the basic problems of 3D geological information science. To address the problem of expressing complex geological structures by regular grids, PillarGrid, Stack-Based Representation of Terrains (SBRT), etc., this study proposes the InterfaceGrid data model to fully consider that the distribution of geological structures/attributes underground exhibit strong non-uniformity, discontinuity, spatially multi-scaled, and show longitudinal stratification and multi-attribute field coupling. By design, this InterfaceGrid data model can uniformly describe 3D geological structures and realize the vector raster integration expression of complex geological structures. In this paper, the formal expression framework of InterfaceGrid is constructed based on GeoAtom theory; the construction process of the InterfaceGrid model is described; and the data update and spatial query algorithms are designed based on the InterfaceGrid model. The volume visualization and online browsing of geological grid are realized using GPU ray casting and adaptive sampling strategy. Compared with SBRT, InterfaceGrid can more truly describe the geological boundaries and improve the accuracy of 3D structural geological models. The application of InterfaceGrid in the 3D grid construction of the global lithosphere verifies the applicability of InterfaceGrid in the organization and management of large-scale geological data. Compared with PillarGrid, the data volume is reduced by about 1/3 in InterfaceGrid, making it more suitable for the data-intensive geoscience network applications. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Petrogenesis of Paleoproterozoic granites in the Dondo area, northern Angola block: Geological response to the assembly of Columbia Supercontinent LIU Wei, ZHANG Hongrui, LUO Dike, JIA Pengfei, JIN Lijie, ZHOU Yonggang, LIANG Yunhan, WANG Zisheng, LI Chunjia Earth Science Frontiers    2024, 31 (4): 237-257.   DOI: 10.13745/j.esf.sf.2024.2.15 Abstract （839）   HTML （10）    PDF（pc） （7995KB）（450）       Knowledge map    Save The Paleoproterozoic Eburnean orogenic granites are widely exposed in the western part of Angola, offering an ideal setting to study the magmatism and tectonic evolution of the Angola Block. This paper presents systematic studies of petrology, petrogeochemistry, and zircon U-Pb geochronology on the exposed granites in the Dondo area, northern Angola Block. The results indicate that the emplacement ages of porphyritic biotite monzonite granite and biotite monzonite granite in the Dondo area are 1983.3±7.7 Ma and 1956.6±7.5 Ma, respectively, both products of middle Paleoproterozoic magmatic activity. The whole-rock samples are characterized by high SiO2, ALK, 10000Ga/Al, FeOT/(FeOT+MgO), and Zr+Y+Nb+Ce, and low MgO, TiO2, CaO, and P2O5. Trace elements are enriched in Rb, K, Th, U, Zr, and Hf, and depleted in Sr, Nb, Ta, P, and Ti. All samples are enriched in LREE and depleted in HREE, with no significant negative Eu anomaly. The crystallization temperature, calculated using zircon saturation thermometry, ranges from 757 to 889 ℃. Based on these geochemical characteristics, the granites in the Dondo area are classified as A2-type granite. Mineralogical and geochemical features suggest that the porphyritic biotite monzonite granite and biotite monzonite granite were generated by the mixing of crust-derived melts and mantle-derived mafic magma. The similar formation ages within analytical error, identical mineral assemblages, and consistent variations in major and trace elemental compositions indicate that their parental magma originated from a common magma chamber, with lithological differences resulting from melt extraction processes. It is proposed that the magma producing the potassium feldspar porphyry resided in the deep crust for an extended period, leading to stable crystallization of potassium feldspar, increased viscosity and density, and a frozen state of the magma. Subsequent thermal disturbance and volatile enrichment from mantle-derived magma injection rapidly reactivated the frozen magma chamber, resulting in crystal-melt separation. The extracted melt formed biotite monzonite granite, while magma mixed with pre-existing crystals formed porphyritic biotite monzonite granite. Combining regional and global tectonic evolution, it is suggested that the granites from the Dondo area formed in a post-collision tectonic environment between the São Francisco Craton and the Congo Craton. The Paleoproterozoic magmatic events in the Angola Block are likely responses to the Columbia Supercontinent assembly. Table and Figures | Reference | Related Articles | Metrics | Comments（0）

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Structural differences of shale laminae and their controlling mechanisms in the Wufeng-Longmaxi Formations in Tiangongtang, southwestern Sichuan ZHAO Shengxian, LI Bo, CHEN Xin, LIU Wenping, ZHANG Chenglin, JI Chunhai, LIU Yongyang, LIU Dongchen, CAO lieyan, CHEN Yulong, LI Jiajun, LEI Yue, TAN Jingqiang Earth Science Frontiers    2024, 31 (5): 75-88.   DOI: 10.13745/j.esf.sf.2024.6.31 Abstract （825）   HTML （13）    PDF（pc） （23084KB）（135）       Knowledge map    Save The Tiangongtang area in southern Sichuan Basin is a shale gas exploration and development hotspot, famous for the development of large-scale marine deposits with good sedimentary stability and continuity. Focusing on the laminated organic-rich shale of the Wufeng-Longmaxi Formations, this paper clarifies the shale lamination types based on core description and microscopic observation of large and thin sections. By means of geochemical, mineralogical, petrograpic and pore structural analyses and field emission scanning electron microscope observation, the pore structure and reservoir physical properties are revealed. Accordingly, the internal structural differences and control mechanisms of different lamination combinations are revealed. Shales of the Wufeng-Long1-1 submember mainly develops three lamination combinations: graded, massive and sand-mud interbedded. Graded laminated and interlaminated shale assemblages have much higher horizontal permeability than the massive while the latter has the highest vertical permeability; the graded has the best reservoir physical properties. Moreover, the pore volume and specific surface area of fractures show a decreasing trend from the graded to massive to interlaminated. Under the control of sedimentary environment and diagenesis, graded laminated shales with higher TOC and organic-clay laminae have larger effective pore space, higher pore connectivity and larger pore volume than the interlaminated with lower TOC and thick silty and clay laminae. With relatively high organic content and disordered porous media massive shales have better quality effective storage spaces than sand-mud interbedded shales but worse quality than graded laminated shales. Table and Figures | Reference | Related Articles | Metrics | Comments（0）