Earth Science Frontiers

CONTENTS

2024, 31(3): 0-0.

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Geochemical characteristics, genesis and geological significance of Quedingbu-Luqu peridotites in the Xigaze area, middle Yarlung Zangbo suture zone

CHEN Guochao, ZHANG Xiaofei, PEI Xianzhi, PEI Lei, LI Zuochen, LIU Chengjun, LI Ruibao

2024, 31(3): 1-19.
DOI: 10.13745/j.esf.sf.2023.9.42

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The Xigaze ophiolite is a significant feature of the Yarlung Zangbo suture zone, yet its origin and tectonic setting have been subject to debate. This study focuses on the ophiolite in the Quedingbu-Luqu area of Xigaze. Through detailed field geology, petrology, mineral chemistry, and petrochemistry analyses, it is established that the ophiolite predominantly comprises harzburgite with minor occurrences of gabbro, diabase, and basal. A comparison between the Quedingbu and Luqu harzburgite reveals differences in olivine composition, with the former exhibiting lower Fo values, and variations in Al₂O₃ and Cr₂O₃ content in orthopyroxene. Moreover, clinopyroxene displays higher Al₂O₃ and Cr^# values, while spinel shows lower Cr^# and TiO₂ contents. The Quedingbu-Luqu harzburgite is characterized by high MgO content and low Al₂O₃, CaO, and TiO₂ contents. The total rare earth element (REE) contents range from 0.17×10^-6 to 1.63×10^-6, lower than those of primitive and depleted mantle. Luqu harzburgite exhibits high LREE/HREE and (La/Yb)_N ratios, while Quedingbu harzburgite shows lower values. Luqu harzburgite displays a LREE-enriched U-type REE distribution pattern, whereas Quedingbu harzburgite exhibits a LREE-depleted left dipping REE distribution pattern. The large ion lithophile elements Rb and Ba in Luqu harzburgite are higher than in Quedingbu harzburgite, while K and Sr are lower. The Quedingbu-Luqu harzburgite likely originates from spinel lherzolite in the mantle. The mineral chemistry and whole-rock geochemical characteristics of Quedingbu-Luqu harzburgite resemble that of deep-sea mantle peridotite. Quedingbu harzburgite represents residue from 10% to 15% partial melting, while Luqu harzburgite represents residue from 20% to 25% partial melting. The formation of Quedingbu-Luqu harzburgite occurred in a slow to ultra-slow extensional ocean ridge environment. The diversity of the Xigaze ophiolite is closely tied to the degree of partial melting in the source and subsequent melt/fluid metasomatism.

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Geochemical characteristics and petrogenesis of the Neoproterozoic Eshan highly fractionated I-type granites, western Yangtze block

LI Guangjie, CHEN Yongqing, SHANG Zhi, LIU Shibo

2024, 31(3): 20-39.
DOI: 10.13745/j.esf.sf.2023.6.18

Abstract ( 641 )

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The Eshan highly fractionated I-type granites, situated in the western margin of the Yangtze block, represent a significant component of the Neoproterozoic magmatic belt within the region. A comprehensive investigation into their magma source, genesis, and tectonic settings can provide insights into the evolutionary trajectory of the Neoproterozoic crust. This study conducts zircon LA-MC-ICP-MS U-Pb dating and geochemical analyses on the Eshan highly fractionated I-type granites. The results indicate that these granites predominantly consist of red medium-coarse granite and gray-white medium-coarse granite, formed at approximately 746±34 Ma (MSWD=4.2) and 732±30 Ma (MSWD=3.3), respectively. Geochemical analysis reveals a highly fractionated I-type signature characterized by elevated levels of SiO₂ (70.32%-78.41%), Na₂O (3.09%-3.94%), and K₂O (5.13%-7.35%), while exhibiting lower concentrations of CaO (0.52%-0.90%), TiO₂ (0.001%-0.025%), and P₂O₅ (0.061%-0.097%). The rocks exhibit enrichment in K, Rb, Th, and depletion in Nb, P, and Ti. Sr-Nd isotope analysis shows ε_Nd(t) values ranging from -10.8 to -7.5, with two-stage Nd model ages (T_DM2) falling within the range of 2.3 to 2.0 Ga. Integrating these findings with regional geological studies, it is proposed that the Eshan highly fractionated I-type granites originated from the underplating of mantle- and/or juvenile mafic lower crust-derived magma that intruded the upper crust, triggering partial melting of Paleoproterozoic medium- to high-potassium basaltic rocks and biotite gneiss under an extensional tectonic regime. Subsequently, these granites were formed through a process of high fractional crystallization.

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Genetic mechanism of Late Carboniferous intermediate-acid volcanic rocks in southern West Junggar and its constraints on the closure of the Junggar Ocean

ZHI Qian, REN Rui, DUAN Fenghao, HUANG Jiaxuan, ZHU Zhao, ZHANG Xinyuan, LI Yongjun

2024, 31(3): 40-58.
DOI: 10.13745/j.esf.sf.2023.5.30

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Carboniferous magmatic rocks are exclusively discovered in West Junggar, and investigating their petrogenesis and geodynamic mechanisms can offer crucial insights into understanding the Late Paleozoic tectonic framework, evolutionary history, and the closure of the Junggar Ocean. This study presents petrological, geochronological, and geochemical data on Late Carboniferous intermediate-acid volcanic rocks, including andesite, dacitic andesite, rhyolitic dacite porphyry, and rhyolite in the Hala’alate Mountain of southern West Junggar, aiming to elucidate their genetic mechanisms. LA-ICP-MS zircon U-Pb dating of andesite and rhyolite revealed crystallization ages of 308-305 million years ago, indicating the presence of middle to late Late Carboniferous volcanic rocks in West Junggar. These volcanic rocks are geochemically characterized by enrichment in light rare earth elements and large ion lithophile elements, as well as depletion in high field strength elements (such as Nb, Ta). They exhibit high sodium content and low potassium content, falling within the low-K tholeiitic to medium-K calc-alkaline series, resembling island arc volcanic rocks.The andesite and dacitic andesite have high content of SiO₂ (56.15%-66.13%), Al₂O₃ (16.03%-17.94%), Na₂O (3.44%-5.59%), Sr (364-576)×10^-6, high Na₂O/K₂O (3.20-6.40) and Sr/Y (33.5-55.6) ratios, and also exhibit low content of MgO (1.59%-2.68%), Y (10.0-16.0)×10^-6 and Yb (1.08-1.83)×10^-6 with positive Eu anomalies (δEu=1.09-1.22), showing some features of typical adakite in arc settings, and are believed to be derived from the partial melting of subducted oceanic crust in garnet amphibolite-facies without significant interaction with the overlying mantle wedge. Rhyolitic dacite porphyry and rhyolite have high content of SiO₂ (69.59%-75.03%) and total alkali (Na₂O+K₂O: 7.81%-8.89%), and very low content of TFe₂O₃ (0.94%-1.57%) and MgO (0.12%-0.97%) with weak negative Eu anomalies (δEu=0.63-1.00), indicating that they are metaluminous I-type rhyolites, and are probably originated from the partial melting of basaltic lower crust, with addition of a small amount of mantle-derived materials. The findings presented, combined with previously published research in the region, suggest that an island arc-back-arc basin evolutionary system persisted in the study area during the late Late Carboniferous. Furthermore, the closure of the Junggar Ocean in southern West Junggar likely occurred later than the early Early Permian.

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Pore scale simulation study of transverse dispersion of solute in porous media with different cementation degrees

HOU Yusong, HU Xiaonong, WU Jichun

2024, 31(3): 59-67.
DOI: 10.13745/j.esf.sf.2023.9.32

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Deeply understanding and accurately characterizing the transverse dispersion behavior of solutes at the pore scale is crucial for unveiling the internal mechanisms of solute transport phenomena and enhancing the precision of solute transport simulations. In this study, utilizing a pore-scale simulation method, we have investigated the transverse dispersion behavior of solutes in porous media with varying degrees of cementation. The findings of this research are as follows: The transverse dispersion of solutes increases with the cementation degree, although the degree of enhancement is lower compared to longitudinal dispersion. The transverse dispersion does not exhibit a significant scale effect within the range of simulated cementation degrees. The study revealed that the difference between the transverse diffusion coefficient (D_T) and the longitudinal diffusion coefficient (D_L) in all media is not constant but gradually increases, eventually reaching a steady state with solute transport. Both the asymptotic value of D_L/D_T and the time required to reach this value are influenced by the cementation degree. There is a notable discrepancy between assuming D_T to be one order of magnitude smaller than D_L and the actual solute dispersion behavior. By comparing the probability density of the lateral and longitudinal components of flow velocity and the probability density of the advective rate of solutes in different media, this paper elucidates the internal mechanisms underlying the variations in solute transverse dispersion characteristics and highlights the differences between transverse and longitudinal dispersion behaviors.

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Dolomite crystal structure and geochemical characteristics in response to depositional environment: An example of dolomite from the Late Ediacaran Dengying Formation of the Yangzi Plateau

YANG Zhibo, JI Hancheng, BAO Zhidong, SHI Yanqing, ZHAO Yajing, XIANG Pengfei

2024, 31(3): 68-79.
DOI: 10.13745/j.esf.sf.2023.6.16

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The crystal structure and geochemistry of dolomite in the Yangba section of the Late Ediacaran Dengying Formation on the Yangtze Platform are investigated to understand how they reflect the sedimentary environment in the paper. The study involves systematic sampling to analyze the evolution of the sedimentary environment based on petrological and geochemical characteristics. The research aims to elucidate the relationship between the crystal structure of dolomite, its geochemical properties, and the formation environment. The findings indicate the following: (1) The Yangba section of the Dengying Formation predominantly contains various types of microbial dolomite, including stromatolites, oncoids, foam asbestos, thrombolites, as well as some grain, particle, and breccia dolomite. The vertical sequence shows rhythmic layers of multi-stage microbial dolomite, primarily in restricted platform tidal flat and grain beach facies. (2) Geochemical analysis reveals that the Dengying Formation underwent sedimentary evolution in a shallow water environment characterized by arid conditions and high salinity, resulting in the deposition of mud and powder crystal dolomite. The lower part of the second section experienced deepening water conditions with increased humidity and lower salinity, leading to the prevalence of microbial dolomite. The middle and upper parts of the second section had relatively shallower water, decreasing humidity, and slightly higher salinity. In the fourth period, the water fluctuated between deepening and quick shallowing, accompanied by decreasing humidity and increasing salinity. (3) The dolomite crystal structure in the study area indicates the involvement of Mg²⁺-rich fluids. In arid, high salinity environments, there is a/c negative deviation, while in humid, low salinity conditions, there is a/c positive deviation. The order degree distribution suggests that a/c approaches ideal dolomite as the order degree increases. These results not only elucidate the connection between the crystal structure of contemporaneous dolomite and the formation environment but also provide insights into the ancient seawater environment of the late Proterozoic Dengying Formation.

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Quantitative analysis of provenance in the Lower Cretaceous of the northwestern Ordos Basin

LIU Chiheng, LI Ziying, HE Feng, ZHANG Zilong, LI Zhencheng, LING Mingxing, LIU Ruiping

2024, 31(3): 80-99.
DOI: 10.13745/j.esf.sf.2023.6.22

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The Lower Cretaceous represents a significant structural layer in the Ordos Basin, particularly notable for the emergence of sandstone-type uranium deposits in recent years. Understanding the source-sink dynamics during this period offers valuable insights into the tectonic-sedimentary processes triggered by the late Yanshanian orogeny in the western North China Craton, the paleoclimate transition, and the enrichment patterns of sandstone uranium deposits within the Ordos Basin. In this study, we conducted paleocurrent azimuth measurements and detrital zircon U-Pb dating across various strata of the Lower Cretaceous in the northwestern Ordos Basin. Furthermore, we refined the compilation approach for the zircon U-Pb age dataset in the potential provenance area surrounding the basin. Utilizing quantitative analyses, we assessed the detrital contributions from each provenance to the basin. Subsequently, the source-sink system of the Lower Cretaceous in the northwestern Ordos Basin was reconstructed. The results delineate the U-Pb ages of detrital zircons from the Lower Cretaceous into three primary groups: 1.79-1.64 Ga, 2.02-1.82 Ga, and 2.58-2.45 Ga, corresponding to Precambrian ages. Additionally, two major age groups of 336-257 Ma and 476-425 Ma signify Phanerozoic ages. Through quantitative provenance analysis, we identified the Yinshan, Langshan, Zhuozishan-Helanshan, and Alxa regions as collective sediment contributors to the study area, each with varying contribution ratios, indicating a diverse provenance supply. Our study suggests that during the Early Cretaceous, the Yinshan and Langshan regions primarily acted as provenance areas, supplying fluvial deposits to the basin’s interior. In contrast, the Alashan area transported sediments from the northern part of Zhuozishan and the Helanshan peak into the Ordos Basin through aeolian processes. This phenomenon led to the deposition of alternating eolian and fluvial formations in the study area during the Luohe-Lohandong period in the Early Cretaceous.

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Quaternary sequence framework and sedimentary evolution of Qiongzhou Straits

CHEN Fei, ZENG Weite, TONG Changliang, ZHANG Congwei, FU Biao, CHEN Yang, CHEN Bo

2024, 31(3): 100-112.
DOI: 10.13745/j.esf.sf.2024.2.2

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To explore the Quaternary stratigraphic structure and sedimentary evolution process in the Qiongzhou Strait area, the 1140 km high-resolution single-channel seismic profile and 5 borehole core data in the Qiongzhou Strait were interpreted, and combined with grain size analysis, ¹⁴C dating, optically stimulated luminescence dating and microfossil analysis, the characteristics of seismic facies and sedimentary environment were described, and stratigraphic division and correlation were carried out to analyze the variation law of sedimentary environment. The results show that a total of 8 seismic reflection interfaces have been identified on the single seismic section, which are divided into 6 sets of seismic sequences. The overall Quaternary sediment in the Qiongzhou Strait is characterized by “thick in the west and thin in the east”, mainly distributed in the eastern and western mouths of the strait and on the slopes on both sides of the strait. The deepwater area in the central part of the strait has been almost completely eroded by strong currents. Due to frequent fluctuations in sea level, neotectonic movements, and strong hydrodynamic forces, the Quaternary sedimentary environment in the Qiongzhou Strait has undergone complex changes: multiple intercontinental sedimentations occurred during the early and middle Pleistocene periods; during the late Pleistocene, there was a significant interaction between the sea and land in the western part of the strait, while shallow sea deposits dominated the eastern part; several sedimentary hiatuses also occurred during the transgression of the Holocene period.

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Geochronology and geochemical characteristics of the Douya iron-copper polymetallic deposit in the Baoshan block, western Yunnan

LI Fanglan, LIU Xuelong, ZHOU Yunman, ZHAO Chengfeng, LI Shoukui, WANG Jiyuan, LU Bode, LI Qingrui, ZHANG Weiwen, WANG Hai, CAO Zhenliang, ZHOU Jiehu

2024, 31(3): 113-132.
DOI: 10.13745/j.esf.sf.2023.6.17

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The Douya iron-copper polymetallic deposit is a skarn-type deposit located in the northern portion of the Baoshan-Zhenkang lead-zinc polymetallic ore belt. The orebodies are found in the Hetaoping Formation and Shahechang Formation of the Upper Cambrian system, characterized by marbled limestone intercalated with argillaceous limestone. No intermediate-acid rock bodies have been identified within the deposit. To elucidate the age of ore formation, physical and chemical conditions of ore formation, and properties of ore-forming fluids, comprehensive petrographic analysis, geochemical analysis, and LA-SF-ICP-MS U-Pb dating were conducted on garnets from the deposit. The major element characteristics of the garnets from the Douya deposit in the Baoshan block indicate that they belong to the grossular-andradite solid solution series and can be classified into two types: Grt I and Grt II. Variations in temperature and oxygen fugacity within the Douya deposit have influenced the trace element composition, indicating a transition in the pH of the fluid system from early neutrality to late acidity. LA-SF-ICP-MS U-Pb dating of the garnets yielded reliable age data of 468-461 Ma, suggesting that mineralization at the Douya deposit occurred during the Middle Ordovician. The similar rare earth distribution curve and formation age of Shuangmaidi and Qingshuihe granites suggest a potential connection between these deposits and the delamination of the lithospheric mantle. It is proposed that the main source of mineralization in the Douya deposit involves the partial melting of ancient continental crust in combination with materials derived from the mantle.

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Petrogenesis of reductive S-type granites in the Pengshan district, northern Jiangxi Province, and their implications for tin enrichment: Insights from zircon trace elements

YIN Qingqing, TANG Juxing, XIANG Xinkui, ZHAO Xiaoyan, WANG Fangyue, XU Yumin, GUO Hu, YU Zhendong, XIE Jinling, DAI Jingjing, PENG Bo

2024, 31(3): 133-149.
DOI: 10.13745/j.esf.sf.2023.9.3

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The Pengshan tin-polymetallic metallogenic ore field is situated at the transitional junction of the Middle-Lower Yangtze metallogenic belt and the Jiangnan tungsten-polymetallic metallogenic belt. Previous research has indicated that granites associated with large-scale tin mineralization typically stem from highly differentiated peraluminous magmas. However, the precise threshold of oxygen fugacity governing the distribution and migration of tin with mineral phases in reducing magmas remains unknown. It is unclear whether the zonation of tin and tungsten mineralization in northern Jiangxi Province is controlled by the characteristics of the magmatic source or by oxygen fugacity. This study delves into the petrogenesis of granites, the tin source, the redox conditions during the early stages of magmatic evolution, and their influence on the distribution, extraction, and migration of tin within the magma. Through detailed in situ zircon microanalysis of the Pengshan pluton, the findings reveal that the P content of zircon is generally high. The slope of three trend lines fitted by P-(∑REE+Y) is 0.91, 0.85, and 0.81, respectively, aligning with the characteristics of S-type granites (∑REE+Y)<1.15×P. In the Eu/Eu^*-Yb_N/Gd_N diagram, a negative correlation is observed in all rock groups, indicating that the Eu/Eu^* ratios of zircons are constrained by the co-crystallization of titanite and plagioclase. The Hf-Ce⁴⁺/Ce³⁺ zircon and Ti-zircon ratios reflect the degree of reduction in each rock unit within the Pengshan pluton. The zircon Eu anomaly (Eu/Eu^*) and Ce⁴⁺/Ce³⁺ zircon ratio exhibit decreasing trends across the three rock units comprising the Pengshan pluton: post-metallogenic granite porphyry→biotite monzogranite batholith→metallogenic muscovite granite. The sandy-argillaceous sedimentary rocks and spilite formed from marine paleo-volcanic eruptive deposits around 1.5 to 1.3 billion years ago likely served as the initial source of tin in the region. The oxygen fugacity of the muscovite granite is lower than that of the Shimensi deposit, and zircon trace elements indicate that the tin-rich magma possesses lower oxygen fugacity compared to the tungsten-rich magma.

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Potassium and magnesium isotope fractionation during magmatic differentiation and hydrothermal processes in post-collisional adakitic rocks and its indicative significance: A case study of the Qulong porphyry copper deposit, southern Tibet

ZI Yanmei, TIAN Shihong, CHEN Xinyang, HOU Zengqian, YANG Zhiming, GONG Yingli, TANG Qingyu

2024, 31(3): 150-169.
DOI: 10.13745/j.esf.sf.2024.4.22

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The study focused on investigating the behavior of potassium and magnesium isotopes during magmatic differentiation and hydrothermal processes in post-collisional adakitic rocks from the Qulong porphyry copper deposit in southern Tibet. The analyzed rocks included dioritic enclaves, granodiorites, and granite porphyries, with the latter containing a super-large copper deposit. The research confirmed that these rocks likely originated from different degrees of partial melting and fractional crystallization from the same source. The δ⁴¹K values for the dioritic enclaves, granodiorites, and granite porphyries ranged from -0.38‰ to -0.22‰, -0.43‰ to -0.34‰, and -0.59‰ to -0.36‰, respectively. While the variation in δ⁴¹K values among the rock types was small, there was a clear negative correlation between δ⁴¹K and the concentrations of K₂O and SiO₂, indicating potassium isotope fractionation during the migration of potassium in the rocks. The study suggested that the evolution of dioritic enclaves to granodiorites showed a positive correlation between δ⁴¹K and Sc and Y, implying that the separation and crystallization of hornblende played a significant role in potassium isotope fractionation. In contrast, the composition of potassium isotopes varied significantly in granite porphyries. The evolution of granite porphyries displayed a positive correlation between δ⁴¹K and Eu/Eu^* and Sr, suggesting that potassium isotope fractionation in these rocks may be primarily related to the fractional crystallization of plagioclase during late-stage rock evolution. The study also indicated that the observed potassium isotope fractionation in granite porphyries likely resulted from the combined influence of magma and hydrothermal fluid, rather than solely from mineral separation and crystallization processes. The heavier potassium isotopic composition in dioritic enclaves compared to the mantle was attributed to potential factors such as the lower crust having a heavier K isotopic composition than the mantle, and metasomatism of the magma source area by heavy potassium-rich fluid/melt from the subduction plate. In terms of magnesium isotopes, the δ²⁶Mg values for the three types of rocks (dioritic enclaves, granodiorites, and granite porphyries) were similar and fell within the range of the mantle and lower crust. There was no correlation between δ²⁶Mg and MgO or SiO₂ in these rocks, indicating that magnesium isotope fractionation did not occur during the differentiation of adakitic magma, consistent with previous findings on magnesium isotope behavior in granites. Comparing the Qulong porphyry copper deposit in southern Tibet to the Dexing porphyry copper deposit in Jiangxi, both as typical hydrothermal deposits, the study noted that the altered rocks in Dexing showed higher potassium and magnesium isotope values than fresh magmatic rocks, with significant changes in their isotopic composition. In contrast, the potassium and magnesium isotopic compositions of adakitic rocks in Qulong were mostly within the baseline range of magmatic rocks and were not significantly affected by hydrothermal alteration. The study highlighted that the large copper enrichment in granite porphyries at the Qulong deposit was mainly due to the exsolution of magmatic hydrothermal fluid. It suggested the presence of at least two types of hydrothermal fluids with different properties (temperature and salinity) causing local fluctuations in the isotopic composition of potassium and magnesium in the granite porphyries. These fluids not only altered the isotopic composition of potassium and magnesium but also facilitated the extraction of metallic elements from highly evolved magma, ultimately leading to copper mineralization.

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Metallogenic characteristics and ore deposit model of porphyry copper-epithermal gold system in the Duobaoshan ore field, eastern margin of the Central Asian Orogenic Belt

BAI Chenglin, XIE Guiqing, ZHAO Junkang, LI Wei, ZHU Qiaoqiao

2024, 31(3): 170-198.
DOI: 10.13745/j.esf.sf.2023.2.78

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The Duobaoshan ore field, situated in the eastern part of the Central Asian Orogenic Belt (CAOB), represents the largest porphyry Cu (Mo)-epithermal Au metallogenic system with an ancient mineralization age (477-470 Ma) in Northeast China. The reserves of copper, molybdenum, and gold resources have been preliminarily estimated to be over 5 Mt, 0.16 Mt, and 130 t, respectively. Despite this, the metallogenic characteristics and ore deposit model of this system remain unclear. This study comprehensively analyzes the geological, geochemical characteristics, and timing of the deposit. It suggests the presence of two mineralization events in the metallogenic system: the primary episode, occurring in the early Ordovician, and a subsequent superimposed mineralization event in the late Triassic. The mineralization exhibits spatial zonation, with explosive brecciated copper mineralization in the lower part, vein copper mineralization in the middle part, and gold mineralization in the upper part. Wall-rock alteration progresses from the center to both sides or from early to late, transitioning through potassic-biotite, propylitic, clay, carbonate, phyllic, and silicification alteration zones. The ore-forming fluids are identified as magmatic water, transitioning from porphyry copper to epithermal gold deposits or from Duobaoshan to Zhengguang deposits, with a trend of increasing proportions of meteoric water. The high Ce⁴⁺/Ce³⁺ ratios (174-461; average 290) and high $f O 2$ characteristics of the adakitic magma suggest a main mineralization related to crust-mantle mixed-sourced magmatism linked to the subduction of the Paleozoic Paleo-Asian Ocean. Mineralization is controlled by ancient volcanic mechanisms, and the increase in metallogenic depth from northwest to southeast is associated with denudation levels. The presence of the Tongshan reverse fault influences mineralization, indicating the south of the Tongshan fault as a promising exploration target. Furthermore, an ore deposit model for the Paleozoic porphyry copper-epithermal gold system in this region is proposed to guide future mineral exploration efforts.

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The controlling role of magmatic factors on the differential mineralization in the Tongling ore district, eastern China: Evidence from the mineralogy of amphibole and plagioclase

CHEN Ke, SHAO Yongjun, LIU Zhongfa, ZHANG Junke, LI Yongshun, CHEN Yuying

2024, 31(3): 199-217.
DOI: 10.13745/j.esf.sf.2023.12.60

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The Dongguashan Cu (Au) deposit and the Xinqiao S-Fe-Cu-Au deposit are two large skarn-type deposits in the Tongling Ore District. These deposits share a similar metallogenic geological background and are located in the same stratigraphic horizon. However, they exhibit distinct differences in mineral assemblages with the Dongguashan deposit being dominated by chalcopyrite and pyrrhotite, while the Xinqiao deposit is characterized by pyrite and magnetite dominance. The factors influencing these contrasting mineral assemblages remain unclear. To address this scientific question, this study focuses on amphibole and plagioclase in the ore-forming rock masses of both deposits to investigate the magmatic influences on their differential mineralization. Petrographic analysis, EPMA major element analysis, and LA-ICP-MS trace element analysis were conducted on amphibole and plagioclase from the Qingshanjiao quartz monzodiorite of the Dongguashan deposit and the Jitou quartz diorite of the Xinqiao deposit. The results reveal that most amphiboles in the Qingshanjiao rock mass belong to the magnesium amphibole series, whereas those in the Jitou rock mass belong to both the magnesium amphibole and amphibole series. The crystallization pressure, crystallization temperature, crystallization depth, oxygen fugacity and water content of amphibole in the Qingshanjiao and Jitou intrusions are 41-306 MPa and 23-225 MPa, 691-916 ℃ and 634-918 ℃, 1.6-11.6 km and 0.9-8.5 km, ΔNNO=0-2.3 and ΔNNO=-0.4-2.4, 3.7%-5.5% and 3.1%-5.4%, respectively. The amphiboles in both intrusions are predominantly of crustal origin, with some showing characteristics of crust-mantle mixing. Plagioclase in both rock masses is predominantly feldspar. Based on the structure and composition profile of plagioclase, it is suggested that the crystal groups in the Qingshanjiao and Jitou rock masses originate from five and four different magma subsystems, respectively, and have undergone mafic magma injection and mixing. The study proposes that variations in oxygen fugacity and element content in mafic magmas play a key role in controlling the differential mineralization observed in the Dongguashan and Xinqiao deposits.

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The metallogenic series in West Qinling, Gansu Province, and their quantitative estimation

HE Jinzhong, DING Zhenju, ZHU Yongxin, ZHEN Hongxu, ZHANG Wanren, LIU Jie

2024, 31(3): 218-234.
DOI: 10.13745/j.esf.sf.2023.2.68

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This paper is focused on determination of metallogenic series in West Qinling and their different combinations, in which the basic factors are all minerals specified by Chinese Mineral Resources Geology Project, and furtherly makes known their significance in ore-searching by quantitative estimation results. According to the principle for determination of metallogenic series, 21 metallogenic series, and 84 models of a class of deposits were determined based on the distribution characteristics of 39 kinds of minerals in West Qinling of Gansu Province. In the light of metallogenesis, metallogenic setting, and tectonic cycles to which the metallogenic series correspond, 5 metallogenic series assemblages, 12 metallogenic series types, and 4 metallogenic series groups were determined, respectively. As there were sub-tectonic cycles, some sub-metallogenic series groups were recognized in Variscan-Yanshanian tectonic cycle, and furtherly, the evolution regularity of metallogenic series in tectonic cycles was discussed. Two concepts named resources equivalent, and resources equivalent density were put forward; together with other metallogenic extent indices and metallogenic intensity indices, the quantitative estimation of metallogenic series and their different combinations were effectively carried out. The research results are as follows: The metallogenic diversity of metallogenic series is positively correlated to the intensity of intermediate-acidic magmatic activity. The advantaged metallogenic series are Variscan-Indosinian metallogenic series related to magmatism in Middle Qinling, Late Paleozoic sedimentary metallogenic series in Middle Qinling, Variscan-Indosinian ore-bearing fluidization metallogenic series in Middle Qinling, Indosinian-Yanshanian metallogenic series related to magmatism in South Qinling, Paleozoic-Triassic sedimentary metallogenic series in South Qinling, and Variscan-Indosinian ore-bearing fluidization metallogenic series in South Qinling. The advantaged metallogenic series types are those of superimposition of post-collision on foreland basin, and superimposition of post-collision on magmatic arc.

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Metallogenic regularity and prospecting direction of gold deposits in Northeast China

WANG Yan, QIN Yan, LI Hua, WANG Denghong, SUN He, WANG Chenghui, HUANG Fan

2024, 31(3): 235-244.
DOI: 10.13745/j.esf.sf.2023.2.83

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Gold deposits are significant sources of precious metal minerals and play a dominant role in Northeast China. The region boasts rich rock gold resources with a distinct regional concentration trend, particularly in placer gold, making it a key production area in the country. By systematically compiling previous research findings on gold in this region, a comprehensive summary of resource endowment, deposit types, spatiotemporal distribution characteristics, and metallogenic evolution has been presented, along with indications of future prospecting directions. Based on industrial and genetic classifications of gold deposits, those in Northeast China are categorized into placer, magmatic hydrothermal, continental volcanic, metamorphic, porphyry, superposition, and unknown origin flow types. Rock gold is predominantly found in the Liaodong metallogenic belt of the North China metallogenic province, the eastern metallogenic belt of the northern margin of the North China continent, the Xiaoxinganling-Zhangguangcailing metallogenic belt of Jihei metallogenic province, the Jizhong-Yanbian metallogenic belt, and the East Wuzhumuqinqi-Nenjiang metallogenic belt of Greater Khinganling metallogenic province. Placer gold is primarily distributed along the Sanjiang River in Heilongjiang Province, the east Wuzhu Muqin Qi-Nenjiang metallogenic belt in Daxing’anling metallogenic province, the Jiamusi Xingkai metallogenic belt in Jihei metallogenic province, and the Lesser Khingan Mountains-Zhangguangcai metallogenic belt. Gold deposits in Northeast China exhibit characteristics of multi-cycle and multi-stage mineralization, spanning seven ore-forming periods including Archean, Proterozoic, Caledonian, Varissian, Indosinian, Yanshanian, and Himalayan. With 13 ore-forming series, 22 ore-forming sub-series, and 22 third-level prediction areas, the region displays favorable ore-forming conditions and promising prospecting prospects.

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Three-dimensional geological modeling and mineral prospectivity mapping in the Weishancheng gold-silver district, Henan, China

GU Hao, YANG Zeqiang, GAO Meng, TANG Xiangwei, WANG Dongxiao, LIU Kuisong, YANG Shuren, GUO Yueshan, WANG Yun, WANG Gongwen

2024, 31(3): 245-259.
DOI: 10.13745/j.esf.sf.2023.6.8

Abstract ( 674 )

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Three-dimensional (3D) geological modeling and mineral prospectivity mapping have currently emerged as widely adopted and well-developed technical approaches. Leveraging insights from the geological features of the Yindongpo gold deposit and the Poshan silver deposit, the application of 3D modeling and mineral prospectivity mapping has been extended to the Weishancheng district. A comprehensive understanding of geological entities (such as strata, rock formations, and ore bodies) and structural configurations has been achieved through the establishment of 82 geological profiles. Geophysical models encompassing density, magnetic susceptibility, and resistivity have been constructed using 1:50000 gravity and magnetic data along with 63 induced polarization datasets. Additionally, a geochemical model has been developed based on 52 rock survey profiles, 614 boreholes, 117 exploratory trenches, 56 shallow wells, and 94-foot drills. Integration of geological, geophysical, and geochemical datasets has been accomplished through the amalgamation of the data and methodologies. Following the principles of the “Trinity” metallogenic prediction theory, a 3D quantitative prediction model for magmatic hydrothermal gold and silver deposits within the district has been formulated, leading to the establishment of exploration criteria for gold and silver deposits. Utilizing weights of evidence, the weight values and correlation degrees of the exploration criteria have been extracted to facilitate mineral prospectivity mapping. The determination of threshold values via C-V fractal analysis has resulted in the identification of six prospective targets. The application of weights of evidence for 3D mineral prospectivity mapping has been validated as a viable and scientifically sound approach. The delineated targets hold significant practical implications for the exploration of concealed ore bodies within the deep and peripheral regions of mining sites.

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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

2024, 31(3): 260-283.
DOI: 10.13745/j.esf.sf.2023.2.86

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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.

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Volcanic sedimentation of Cretaceous Jiufotang Formation in the Chaoyang Basin and its impact on organic matter enrichment

ZHANG Jiazhi, JIANG Zaixing, XU Jie, WEI Siyuan, SONG Lizhou, LIU Tong, SHEN Zhihan, JIANG Xiaolong, LI Yongfei, ZHANG Xi

2024, 31(3): 284-297.
DOI: 10.13745/j.esf.sf.2023.9.22

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The Chaoyang Basin in western Liaoning, situated in the eastern section of the Yanshan tectonic belt, is a fault basin from the Mesozoic era on the periphery of Songliao. The level of exploration understanding in this region is relatively low. Previous studies on the Lower Cretaceous Jiufotang Formation in the Chaoyang Basin primarily focused on lacustrine deposits, overlooking the significant impact of volcanic events on the basin’s sedimentation. To address this gap, regional geological data investigation, drilling core description, core thin section data observation, and test data analysis were conducted. By classifying pyroclastic rocks into sedimentary pyroclastic rocks and pyroclastic sedimentary rocks based on their content and subdividing them into 11 lithofacies types and 9 lithofacies combinations according to particle size, composition, and sedimentary structure characteristics, five causal mechanisms were proposed: pyroclastic flow, volcanic hyperpycnal flow, volcanic ash heterogeneous light flow, hydrothermal intrusion, and microbial induction. The establishment of the volcanic-lake sedimentary model of the Jiufotang Formation in the Chaoyang Basin, based on volcanic sedimentary sequences and core observation findings, offers a theoretical foundation for oil and gas resource exploration and development in the area. Research indicates that volcanic material positively influences organic matter enrichment in the lake basin. Geochemical tests on source rocks of the Jiufotang Formation in the Chaoyang Basin revealed that samples containing volcanic fine particles involved in sedimentation exhibited better organic matter abundance and enrichment. Given the similar volcanic activity geological background in other basins within the Yanshan tectonic belt, these findings also serve as valuable comparative references for sedimentology and oil and gas resource research in those regions.

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Study on tectonic fracture characteristics and stage evolution of Longmaxi shale reservoir in Yongchuan, southeastern Sichuan Basin

HE Jianhua, LI Yong, DENG Hucheng, WANG Yuanyuan, MA Ruolong, TANG Jianming

2024, 31(3): 298-311.
DOI: 10.13745/j.esf.sf.2023.3.2

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Development characteristics and formation stages of natural fractures are of great significance to shale gas accumulation in the complex structural area of southeastern Sichuan. It also significantly influences the effects of hydrofracturing reconstruction and high gas production of shale reservoirs. Currently, there is no systematic study on the characteristics and evolutions of natural fractures with various origins in deep shale gas blocks far from the basin margin in the southeastern Sichuan Basin, which hinders the efficient exploration and development of deep shale gas reservoirs in the basin. Based on field outcrops, drilling cores, thin sections, geochemical data, and apatite dating, the characteristics and formation stages of natural fractures in the Longmaxi Formation shale reservoirs in the Yongchuan area have been studied. The results indicate that the Longmaxi Formation shale mainly developed tectonic fractures, including shear fractures with medium to high angles, low angle slip fractures, and vertical tensile fractures. Additionally, bedding fractures and overpressure fractures are also observed in the cores, with hydrothermal dissolution fractures mainly developed near the main fault zones. Vertically, the density of fracture development gradually decreases from deep to shallow due to variations in mineral compositions. Horizontally, fractures with high angles, distinct single fracture groups, and high vertical penetration capacity are densely developed in the anticline core or wing steep slope area, while fractures with low angles, small scales, and various fracture groups are developed in the gentle areas. Three tectonic movements—the late Yanshan (86-47 Ma), early to middle Himalayan (47-24 Ma), and late Himalayan to present (24-0 Ma)—contributed to the tectonic fractures in this area. The fracture development and filling characteristics in different evolutionary stages are notably different. The study establishes a tectonic fracture development and evolution model of shale in three phases in the Yongchuan area, providing valuable insights into the study of shale gas enrichment and preservation, as well as a deeper understanding of the evolution of shale fractures in the Longmaxi Formation, southeastern Sichuan Basin.

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The impact of diagenetic fluids on the structural fracture filling and dissolution alteration of ultra-deep tight sandstone reservoirs: a case study of the Kelasu oil and gas field in the Tarim Basin

WANG Junpeng, ZENG Lianbo, XU Zhenping, WANG Ke, ZENG Qinglu, ZHANG Zhiyuan, ZHANG Ronghu, JIANG Jun

2024, 31(3): 312-323.
DOI: 10.13745/j.esf.sf.2024.1.51

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The Kelasu oil and gas area in the Tarim Basin serves as a significant gas source for the “West East Gas Transmission” project in China and stands as the largest ultra-deep oil and gas field developed in the country. The primary reservoir formation targeted in this region is the Cretaceous Bashjiqike Formation, characterized by medium-thick fine to medium sandstone interbedded with thin mudstone layers. Burial depths typically range between 6000 m and 8000 m, and the reservoir matrix’s porosity generally remains below 10%. The pore-throat structure is intricate, with widespread development of structural fractures. The presence of an effective fracture network is essential for achieving high and consistent gas production from this type of reservoir. In the context of deep burial, high temperatures, and pressures, the rapid activity of diagenetic fluids along fractures significantly influences the effectiveness of reservoir fractures. This article conducts microscopic experimental analyses, including CT scanning, main thin section analysis, cathodoluminescence, laser confocal scanning, and scanning electron microscopy on numerous underground rock core structural fractures. The study systematically investigates the diagenetic types of fluids, their configuration relationships, effective fracture openings, and impact distribution range at various scales—from micro-fracture to core fracture, trap, and oil and gas field scales. The impact of diagenetic fluids on the effectiveness of structural fractures within the Cretaceous Bashjiqike Formation of the Kelasu oil and gas field primarily manifests in the cementation, filling, and dissolution of the fracture surfaces themselves and the surrounding reservoir pores. The cementation filling rate of the main fractures, exceeding 60%, typically remains below 5%, with effective openings ranging from 0.2 mm to 2 mm. Diagenetic fluids precipitate or dissolve along microcracks, affecting an approximate range of 4mm to 20 mm around the fractures. Dissolution tends to occur between different minerals in the rocks, particularly quartz and feldspar particles. Vertically, diagenetic fluids follow the fracture network within the upper and middle parts of the anticlinal reservoir, where both cementation and dissolution processes take place. The overall filling rate ranges from 60% to 80%, with the cementation filling rate of fractures in the lower water layer reaching 60% to 90%. Horizontally, diagenetic fluids migrate along the paths of previous sedimentary water systems and structural fractures, with a north-south influence distance spanning 20 km to 40 km, predominantly filled and cemented with calcite. Given the efficient communication of the fracture network in the middle to upper part of the target layer, drilling and completion operations are recommended in these sections to avoid the “basal cementation” layer at the top. In the northern block, acid fracturing techniques are employed to enhance the overall permeability of the reservoir by targeting the large opening fractures filled with calcite material.

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Development characteristics and controlling factors of bedrock weathering crust reservoirs in the northern belt of the Dongying sag

ZHU Maolin, LIU Zhen, LIU Huimin, ZHANG Pengfei, ZHAO Zhen

2024, 31(3): 324-336.
DOI: 10.13745/j.esf.sf.2023.2.65

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The discovery of the Wangzhuang buried-hill reservoir in the western section of the northern belt of the Dongying sag highlights the significant oil and gas exploration potential of Archean bedrock reservoirs. Based on data from outcrops, cores, thin sections, logging, imaging logging, porosity, permeability, and oil testing, this paper summarizes the development characteristics of Archean bedrock weathering crust reservoirs in the Dongying sag. It also delves into the main controlling factors. The results indicate: (1) Archean bedrocks mainly consist of monzogranite and granodiorite, with locally developed granite gneiss. These rocks are brittle and prone to fracturing, providing a lithological basis for high-quality reservoir formation. (2) Vertically, the bedrock weathering crust reservoirs can be categorized into three types: disintegration reservoirs, dissolution-disintegration reservoirs, and eluvial-disintegration reservoirs. (3) Disintegration reservoirs are primarily composed of structural fractures, dissolution fractures, and joint fractures. They exhibit poor physical properties with an average porosity of 2.2% and permeability of 0.25 mD, mainly concentrated in the upper part of the structure. Dissolution-disintegration reservoirs display a distinct double-layer structure. The overlying dissolution layer is 50-150 m thick with good physical properties, including dissolution pores and enhancement fractures, resulting in an average porosity of 4.7% and permeability of 1.3 mD. The underlying disintegration reservoirs have poor physical properties and are dominated by fractures, primarily located in the middle and lower parts of the structure. Eluvial-disintegration reservoirs are characterized by a thin upper layer and a thick lower layer. The overlying eluvium is 10-43 m thick, loose, and fragmented. The reservoir spaces are mainly composed of dissolution cavities, with an average porosity of 4.5% and permeability of 1.7 mD. The underlying disintegration layer is dense with a massive structure, and the reservoir spaces are primarily fracture-dominated, mainly distributed in the gentle slope belt near the higher part of the structure. (4) The physical properties and distribution of bedrock weathering crust reservoirs are controlled by four main factors: the presence of high brittle minerals in rocks influences fracture development, tectonic stress affects fracture formation and distribution, a developed fault system accelerates the formation of effective reservoirs, and paleo-elevation determines the distribution of bedrock weathering crust reservoirs. These research findings are crucial for evaluating bedrock weathering crust reservoirs and guiding oil and gas exploration in the Dongying sag and other faulted basins.

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Volcaniclastic architectures in the Chengdu-Jianyang Area of the Emeishan Large Igneous Province: Identification, Generation Mechanism Interpretations, and Petroleum Reservoir Impact Assessment

LIU Ran, ZHU Bei, QIU Nansheng, LI Ya, WANG Wei, PEI Senqi

2024, 31(3): 337-351.
DOI: 10.13745/j.esf.sf.2023.2.80

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The Permian Emeishan Large Igneous Province represents the aftermath of the most significant Phanerozoic volcanic eruption in China. Recent petroleum exploration within the middle Permian system of the Sichuan Basin has unveiled novel volcaniclastic architectures in the Chengdu-Jianyang Area, situated at the northernmost edge of the Emeishan Large Igneous Province. This study introduces a comprehensive interpretation of the lithology and petrography of these architectures, identifying three primary lithological series: the ignimbrite series, the autoclastic series, and the agglomerate series within the reservoir section. It is proposed that these series originate from terrestrial pyroclastic flows, autobrecciation of effusive lavas, and Strombolian-Hawaiian fire fountaining spattering, respectively. These mechanisms are conclusively established for the first time in this region. The predominant pore spaces within these lithologies are characterized by dissolved and intercrystalline pores formed during alteration processes. The genesis of these lithologies imposes essential constraints on the formation of pore spaces, primarily due to: (1) the production of significant juvenile clasts by these mechanisms; (2) the clastic support of the volcaniclasts maintaining substantial initial porosity and permeability, facilitating hydrothermal fluid interaction with the clast framework; and (3) their proximity to volcanic vents, suggesting accumulation under atypical thermal gradients, leading to heightened activity of altering fluids. These factors culminate in substantial rock framework alteration, laying the groundwork for the development of extensive volcanic petroleum reservoirs.

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Late Cretaceous transgression in the Muglad Basin of Central Africa and its implication for oil and gas exploration

XIAO Hong, LI Meijun, CHENG Dingsheng, LIU Jiguo, LI Jin, XING Xiangrong

2024, 31(3): 352-359.
DOI: 10.13745/j.esf.sf.2023.6.19

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The global transgression during the Late Cretaceous was previously believed to have primarily affected the northern African continent, with the Muglad Basin in the central African region thought to have been unaffected by this event. Within the basin, only one set of organic-rich source rock was known to have formed, namely the lacustrine mudstone of the Lower Cretaceous Abu Gabra Formation. This study collected mudstone samples from both the Upper Cretaceous Darfur Group and the Lower Cretaceous Abu Gabra Formation. Analysis revealed that the mudstones from the Upper Cretaceous Darfur Group exhibit a distinct distribution of dinosteranes and tricyclic terpanes compared to the lacustrine source rocks of the Lower Cretaceous Abu Gabra Formation, showing an abundance of dinosteranes and C₂₃ tricyclic terpanes, which are likely products of transgression. This study suggests that the mudstones from the Upper Cretaceous Darfur Group were influenced by seawater from the Neo-Tethys Ocean, indicating that the global transgression in the Late Cretaceous extended into the Muglad Basin in Central Africa. Furthermore, the presence of organic-rich marine mudstones in the Darfur Group suggests that the basin not only accumulated the lacustrine source rock of the Abu Gabra Formation but also potentially deposited a set of marine source rock. The discovery of marine oil in the K-1 well further confirms the hydrocarbon generation potential of marine source rock in the Darfur Group, pointing to new prospects for petroleum exploration in the Muglad Basin in the future.

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Variability in spatiotemporal groundwater nitrate concentrations in the northeast Ganfu Plain

HE Jiahui, MAO Hairu, XUE Yang, LIAO Fu, GAO Bai, RAO Zhi, YANG Yang, LIU Yuanyuan, WANG Guangcai

2024, 31(3): 360-370.
DOI: 10.13745/j.esf.sf.2023.2.84

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Groundwater in the Ganfu Plain exhibits high NO₃^- concentrations, yet few studies have investigated the seasonal variations and influencing factors of groundwater chemistry, particularly NO₃^- concentrations. In this study, groundwater samples were collected in the northeast region of the Ganfu Plain during both dry and wet seasons. The study aimed to explore the spatiotemporal variations in groundwater chemistry, focusing on NO₃^- concentrations, and the sources of NO₃^- in groundwater using hydrochemical diagrams, Self-Organizing Map (SOM), spatial autocorrelation analysis, and an inverse geochemical model. The results indicate that the primary groundwater types in the study area are Cl·NO₃-Ca and HCO₃-Ca. Human activities emerge as the key factor driving spatial variations in groundwater chemistry. Regions with elevated NO₃^- concentrations and significant seasonal variations are predominantly located in the lower reaches of Nanchang. Conversely, areas with lower NO₃^- concentrations and seasonal variations are primarily situated in the western and southeastern mountainous regions and the lower reaches of the Ganjiang River Delta. The spatial distribution and seasonal variability of groundwater NO₃^- concentrations in the study area are influenced by groundwater runoff conditions, redox environments, and land use patterns. Industrial and domestic sewage are identified as the main sources of NO₃^- in groundwater, with the impact of fertilizers on NO₃^- concentrations also warranting consideration. The results from the inverse geochemical model provide quantitative insights into the effects of water-rock interactions and human activities on groundwater quality during groundwater movement processes.

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Risk assessment of groundwater arsenic in Hetao Basin base on ensemble learning optimization

FU Yu, CAO Wengeng, ZHANG Chunju, ZHAI Wenhua, REN Yu, NAN Tian, LI Zeyan

2024, 31(3): 371-380.
DOI: 10.13745/j.esf.sf.2023.2.40

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The shallow groundwater arsenic pollution in Hetao Basin seriously exceeds the standard, and its potential pollution risk poses a serious health threat to local residents. At present, the perception of the risk distribution of high arsenic groundwater is still insufficient on the macroscopic scale. Based on 605 shallow groundwater samples and environmental factors such as sedimentary environment, climate, human activities, soil physical and chemical characteristics, and hydrogeological conditions as data sources, Random Forest (RF), Extreme Gradient Boosting (XGBoost), and Support Vector Machine (SVM) were selected as the base learners, and Linear Discriminant Analysis (LDA) was selected as the meta-learner to construct a Stacking ensemble learning model for high arsenic groundwater. The ensemble learning model was used to predict the risk distribution of high arsenic groundwater and identify the key environmental factors affecting the risk distribution of high arsenic groundwater in the region. The research showed that the groundwater arsenic concentration exceeded the standard rate (>10 μg/L) was 49.59%, mainly concentrated in the paleochannel zone and flood fans of the Yellow River. The Stacking ensemble model had higher reliability than the RF model with the best performance in the single model, and the Area Under the ROC Curve (AUC) and accuracy were increased by 1.1% and 3.2%, respectively. The high-risk area reached 5257 km², accounting for 38.44% of the total area of the study area. The sedimentary environment is the key environmental factor affecting the risk distribution of high arsenic groundwater, contributing up to 25.06% to the accuracy of the model. The results of this study can provide a method and reference for mapping the spatial distribution of high arsenic groundwater pollution and have important implications for the safety of drinking water and human health in the region.

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K_d-based transport modeling of uranium in groundwater at an acid leaching uranium mine

YANG Bing, MENG Tong, GUO Huaming, LIAN Guoxi, CHEN Shuaiyao, YANG Xi

2024, 31(3): 381-391.
DOI: 10.13745/j.esf.sf.2023.2.69

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Uranium (U) contamination of groundwater at in-situ leaching uranium mines is a global environmental geological problem. Accurately predicting the transport range of U in the groundwater outside the in-situ leaching mining areas is crucial to radiation risk assessment. In this study, the migration range of groundwater U at different production times was quantitatively simulated and predicted by numerical simulation method from an acid in-situ leaching uranium mine. The numerical simulation results showed that the mining activities of in-situ leaching uranium significantly changed the groundwater flow field in the mining area, and depression cones were induced by the high ratio of pumping to injection inside the mining area. On the basis of flow modeling, the transport model of groundwater U without considering adsorption and the retardation transport model based on K_d value were established. According to the groundwater pH of production well and monitoring wells at different distances outside the mining area, different K_d value was assigned by regions. By comparing the simulation results of the two models, it could be found that when considering the adsorption-retardation effect of aqueous medium on groundwater U, the simulation results could be better fitted with the field monitoring data, indicating that the migration of U in groundwater was significantly retarded by the aqueous medium. The U reactive transport model showed that the migration distance and range were reduced by 53% and 41%, respectively. Besides, the model predicted that the migration distance of groundwater U in the mining area was 50 m after 5 years of mining, which was consistent with the monitoring results. It was proven that the numerical simulation method, as an effective tool, could be successfully used to predict the impact of in-situ mining on groundwater environment at the uranium mining site.

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Geophysical analysis of heat source composition in the Fujian coastal geothermal anomaly area

ZHANG Jian, HE Yubei, FAN Yanxia

2024, 31(3): 392-401.
DOI: 10.13745/j.esf.sf.2023.6.15

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The Fujian geothermal anomaly area represents a significant geothermal anomaly region located in the southeastern coastal zone of China. The formation mechanism and composition of heat sources in this area have long been a focal point of theoretical and applied geothermal research. By utilizing thermal, seismic, magnetic, and gravity data, this study examines the heat source composition and genesis of the geothermal anomaly in the Fujian region. The analysis reveals the presence of a shear wave “low-velocity corridor” in the upper crust of the Fujian coastal area, which is associated with a regional listric thrust fault comprising the Zhenghe-Dabu fault zone and the Binhai fault zone. The eastern end of the listric thrust fault connects to the high-temperature zone in the Pacific, while the western end links to the geothermal anomaly area along the Fujian coast. The temperature gradient from the Curie depth to the Moho suggests a lack of conditions for abnormal heat source formation from modern intrusive rock masses. Notably, the radioactive heat generation from granite plays a crucial role in the thermal anomaly observed in this region, with the depth of the radioactive element heat source being less than 5 km. Groundwater acts as a conduit for absorbing radioactive heat from the surrounding rock along thermal conductivity structures, leading to the accumulation of heat and the formation of high-temperature centers. It is proposed that the geothermal anomaly area in the Fujian coastal region is influenced by both deep-seated and shallow heat sources. The deep heat source originates from the high-temperature magma in the Pacific Ocean, transmitted to the surface along the listric thrust fault. In contrast, the shallow heat source arises from the radioactive elements present in granite, with groundwater facilitating its transport to the geothermal field center. In summary, the heat in the Fujian coastal geothermal anomaly area is a result of the combined effects of deep-seated high-temperature magma and shallow radioactive heat sources. The upward transfer of heat from the deep source along the thrust fault, coupled with the collection of shallow heat by groundwater, contributes to the thermal dynamics of the region.

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Quantitative analysis of scaling tendency of karstic geothermal water coupled with CO₂ degassing

LÜ Lianghua, WANG Shui

2024, 31(3): 402-409.
DOI: 10.13745/j.esf.sf.2023.2.82

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Low-to-medium temperature fluid reservoirs hosted in carbonate rocks represent a promising yet relatively unknown hydrothermal geothermal system. Scaling of geothermal water, particularly underground scaling, poses a significant challenge in the sustainable utilization of geothermal resources. To address the limitations of current methods for analyzing karstic geothermal water scaling trends, a chemical thermodynamic simulation approach was employed to develop an enhanced method for quantitatively assessing scaling trends in geothermal water, considering CO₂ degassing effects. This study focused on the influence of CO₂ degassing on scaling trends. The scaling tendency of the Tangshan karstic geothermal area in Nanjing was quantitatively analyzed using the improved method. Results indicate that the geothermal water in the Tangshan area exhibits a propensity for carbonate scaling at the wellhead, primarily composed of CaCO₃, and varying degrees of sulfate scaling in the middle and lower sections of the wellbore, with main components including CaSO₄, SrSO₄, and BaSO₄. By addressing the limitations of existing scaling trend analysis methods, this study offers a theoretical foundation and methodological guidance for scale prevention and removal, thereby facilitating the sustainable utilization of geothermal water resources.

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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

2024, 31(3): 410-419.
DOI: 10.13745/j.esf.sf.2023.2.47

Abstract ( 883 )

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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.

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Pollution characteristics, potential ecological risks and sources of heavy metal pollution in lake sediments in Huoqiu County

LIU Hai, WEI Wei, SONG Yang, PAN Yang, LI Yingchun

2024, 31(3): 420-431.
DOI: 10.13745/j.esf.sf.2023.2.77

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The contents of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) in surface sediments of Chengxi Lake and Chengdong Lake were measured To understand the pollution characteristics, spatial distribution, potential sources, and ecological risks of heavy metals in surface sediments of Chengxi Lake and Chengdong Lake in Huoqiu County. The soil accumulation index, pollution load index, potential ecological hazard index, and sediment quality reference method were used to evaluate the pollution degree and potential ecological hazard of heavy metals. The sources of heavy metals were analyzed by correlation analysis, cluster analysis, and principal component analysis. The results showed that except for Cd, Hg, Pb in Chengdong Lake and Hg in Chengxi Lake, the average values of other elements exceeded the background values, and the content of heavy metals showed significant spatial variability, decreasing from north to south. The soil accumulation index indicates that Ni and Zn in sediments of Chengxi Lake are in a state of unpolluted to moderate pollution. The pollution load index indicates that the sediments of Chengxi Lake are in a state of moderate pollution, and the sediments of Chengxi Lake and Chengdong Lake are in a state of mild ecological risk. The results of heavy metal traceability analysis show that Cr, Zn, Ni, and Cu in the sediments of Chengxi Lake and Chengdong Lake are mainly from the parent material, mineral exploitation, and aquaculture, while As, Pb, Hg, and Cd are mainly from agricultural pollution and domestic sewage. The results can provide a scientific basis for the prevention and control of heavy metal pollution in Chengxi Lake and Chengdong Lake.

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Geophysical dynamic monitoring and analysis of in-situ remediation process at organic contaminated sites

XIA Teng, ZHANG Jiaming, LI Shupeng, GUO Lili, WANG Qi, MAO Deqiang

2024, 31(3): 432-442.
DOI: 10.13745/j.esf.sf.2023.3.1

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Real-time monitoring of in-situ remediation processes is crucial for evaluating the progress and effectiveness of addressing organic contamination at sites. Electrical resistivity tomography, in conjunction with sampling analysis, is utilized to monitor in-situ thermal oxidation remediation procedures. The findings demonstrate that changes in resistivity align with variations in hydrochemistry, groundwater levels, contaminant concentrations, and temperature. Specifically, resistivity decreases as temperature rises during in-situ thermal remediation. By establishing an empirical link between temperature and resistivity, an influence coefficient of concentration on resistivity is proposed, with the coefficient increasing as contamination concentration decreases. Furthermore, the distributions of temperature and contaminant concentrations during the heating phase are inferred, showing a decrease in concentration with increasing temperature. Additionally, variations in resistivity effectively map out the dynamic injection process of persulfate and water during in-situ chemical oxidation remediation. In summary, geophysical methods offer an effective means to dynamically monitor in-situ remediation processes at organic contaminated sites.

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Spatio-temporal evolution evaluation of geological environment of large open-pit coal mine areas in Xilin Gol league

HE Hui, MU Wenping, ZHANG Xiao, SONG Yubing, LÜ Yuanyang, WU Xiong, YE Baoying, BAI Zhongke

2024, 31(3): 443-457.
DOI: 10.13745/j.esf.sf.2023.6.28

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After more than 20 years of development in the large open-pit coal mine areas in Xilin Gol league, Inner Mongolia, a series of mining geological environmental problems have been generated and the geological environment of the mine area has been damaged to some extent, therefore, the evaluation of the spatial and temporal evolution of the geological environment of the large open-pit coal mine areas can provide a reference for the ecological and geological environment restoration of the mine areas. This study evaluates the spatial and temporal evolution of the geological environment in three large mining areas in Xilin Gol league. Firstly, through site investigation, it was clarified that the main mining geological environment problems in the study area mainly include four categories, such as vegetation coverage decline, land occupation (drainage field and industrial sites), topography landscape destruction (open-pit mining) and aquifer destruction. Then remote sensing images were used to quantitatively obtain information on mine geological environment problems between 2000 and 2020, and a mining geological environment evaluation index system was established. After that, the hierarchical analysis was applied to determine the weights of various geological environmental problems, and the impact index model based on GIS was used to evaluate and zone the impact of mine geological environment and explore the law of spatial and temporal evolution of mine geological environment. The results of the study show that: (1) The decreasing vegetation coverage, the area of the land occupied by the soil discharge site and the area of the open pit destroying the landscape of topography and geomorphology are increasing with time in the three large mining areas. (2) The impact of mining on the geological environment in the large mining area is divided into five class sub-areas: no impact area, slight impact area, general impact area, stronger impact area and strong impact area. (3) The spatial and temporal evolution pattern of the geological environment in the three large mining areas is basically the same, and the spatial distribution characteristics and the area change pattern of different impact areas with time are different.

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Research on paths to realize the values of ecological products in national parks based on the geological and nature environmental settings of the China National Parks

MA Junjie, CHENG Jie, LIU Xiaohong, SUN Hongyan

2024, 31(3): 458-469.
DOI: 10.13745/j.esf.sf.2024.1.50

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Establishing National Parks in China is a crucial initiative for biodiversity conservation. It is essential to maximize the value of ecological products within them, benefit society, and promote a sustainable cycle of natural resource conservation and utilization to ensure the high-quality and sustainable development of these parks. Therefore, studying the pathways for realizing the value of ecological products is significant. This paper analyzes the geological settings, environmental conditions, and natural resources of the first batch of five National Parks in China (Three Rivers Source, Giant Panda, Northeast China Tiger and Leopard, Wuyishan, and Hainan Tropical Rainforest National Parks) and discusses the relationship between natural resources and ecological products in these parks. The ecological products are categorized as natural, semi-natural, and artificial based on human interference. Using land and water resources as examples, the paper explores the main factors influencing the value of ecological products and the various types of ecological products that natural resources can be transformed into. Additionally, based on the characteristics of ecological products, the paper presents three levels of pathways and methods for realizing their value and discusses the differences in value realization pathways for ecological products in national parks with diverse geological and natural backgrounds.

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Formation mechanism and tectonic implication of Xinyi earth fissures in Tan-Lu fault transition section

XU Jishan, PENG Jianbing, SUI Wanghua, AN Haibo, LI Zuodong, XU Wenjie, DONG Peijie

2024, 31(3): 470-481.
DOI: 10.13745/j.esf.sf.2023.10.36

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The Xinyi area is located in a crucial transitional zone of the Tan-Lu Fault Zone. Since the 1970s, a total of 28 earth fissures have been discovered in this region. These fissures are mainly concentrated in the area west of Nanmaling Mountain and east of Yihe River-Luoma Lake, covering an affected area of approximately 100 km². The formation of Xinyi earth fissures is closely linked to the stratigraphic structure, seismic activity, and groundwater exploitation, leading to various perspectives on the subject. Recent on-site investigations and exploration methods have revealed the fundamental characteristics of Xinyi earth fissures, including consistent strike, longitudinal pinchout, and localized mass occurrence. These features align closely with the adjacent fault (secondary fault F3 of the Tan-Lu Fault Zone) and are classified as regional tectonic-type earth fissures. Drawing on the geological structure of the Xinyi area, a physical experimental model was developed to simulate the formation of earth fissures under reverse fault action. The experimental findings suggest that fissure development areas are delineated on the ground surface, progressing through stages of shear-cracking, separation, and “bending-cracking” with increasing fault displacement of the reverse fault. Considering the “graben-horst-graben” composite structure in the Xinyi area, the genesis of Xinyi earth fissures can be conceptualized as a seesaw-style tectonic model. Tectonic stress, gravity stress, groundwater fluctuations, among other factors, compress the subsidence section while causing bending and cracking in the rising section, ultimately resulting in the formation of earth fissures. The investigation of earth fissures in the Xinyi area holds significant importance in elucidating structural changes within the “north-middle-south” segment of the Tan-Lu Fault Zone and the interconnected “deep-shallow-surface” structural configurations.

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Research on the 3D implicit potential field modeling method for urban underground space based on the open-source GemPy

LIAO Zhou, LI Mei

2024, 31(3): 482-497.
DOI: 10.13745/j.esf.sf.2024.2.30

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Three-dimensional geological modeling is essential for urban subterranean space planning and management. In the era of geological big data, there is a shift towards implicit modeling techniques. While commercial software like GeoModeller and Surpac offer implicit modeling capabilities, they are proprietary and lack open-source accessibility. This paper focuses on the open-source GemPy modeling platform, utilizing three-dimensional implicit potential field modeling techniques and presenting an algorithmic solution for geological pinch-outs. The proposed approach is integrated into GemPy’s foundational modeling architecture. Through a case study of a specific urban area, the paper demonstrates the workflow for fine-scale three-dimensional geological modeling. A modeling dataset is created using borehole data and the potential field method, along with pan-Kriging interpolation, to establish a three-dimensional geological model of the urban area. Specialized techniques are employed to address urban pinch-outs. To visualize geological interfaces in the model, 18 engineering geological layers are individually displayed. The model’s accuracy is assessed using stratified K-fold cross-validation, including metrics like the Pearson correlation coefficient (CC). Experimental results show that the three-dimensional implicit potential field geological modeling method in GemPy is suitable for urban geological structures, providing a reliable foundation for decision-making in urban subterranean development.

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Rock and mineral thin section identification based on deep learning

ZHANG Lijun, LU Wenhao, ZHANG Jiandong, PENG Guangxiong, BU Jiancai, TANG Kai, XIE Jiancheng, XU Zhibin, YANG Haiyan

2024, 31(3): 498-510.
DOI: 10.13745/j.esf.sf.2023.6.7

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Rock-mineral microscopic image identification is one of the basic means of rock and mineral identification, which is of great significance to the exploration of geological resources. Thin-section microscopic images are generally carried out in the laboratory. This work is tedious and time-consuming, requires a lot of human resources, and the accuracy is limited by the experience of the expert. Deep learning intelligent image recognition algorithm can extract the deep features of microscopic images by convolutional neural network, to achieve the purpose of fast and accurate classification and recognition of microscopic images. In this study, the PyCharm platform is used as the deep learning framework, and the data set that can be applied to the classification and recognition of rock-mineral microscopic images is made based on six data sets such as the teaching rock slice dataset of Nanjing University and the Carboniferous limestone microscopic image dataset of South North China on the China Science Data Network. We design a VGG convolutional neural network model. The model can analyze the feature information in the deep layer of the whole rock slice image and the single mineral image respectively, to achieve the purpose of identifying rock slices. The test results show that with the increase of model training times, the loss function between the predicted value and the real value is decreasing, and the recognition accuracy is increasing. After 50 and 30 cycles of training, the loss function and recognition accuracy of the model have been basically convergent. The recognition success rate of the model for the microscopic image test set is higher than 90%, indicating that the model has a good feature extraction effect for the image and can complete the task of rock-mineral microscopic image recognition. Through the research of this paper, it can be realized that deep learning has high efficiency and accuracy for dealing with such tasks as rock and mineral identification. Developing relevant models and applying them to front-end software can speed up the speed of mineral resources exploration and has important application significance for production practice.

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Analysis and discrimination of tectonic settings based on stacking quantum neural networks

ZHANG Jiawen, LI Mingchao, HAN Shuai, ZHANG Jingyi

2024, 31(3): 511-519.
DOI: 10.13745/j.esf.sf.2023.3.3

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Quantum geoscience represents a cutting-edge interdisciplinary field that leverages quantum computing and quantum machine learning algorithms to revolutionize the analysis of geological data. Among these advancements, the quantum neural network stands out for its efficiency and accuracy in processing complex multi-source data. This study focuses on addressing the challenge of discriminating tectonic settings, enhancing the quantum neural network (S-QNN) with an ensemble strategy to differentiate between basalt, gabbro, and spinel settings. Comparative analyses are conducted with four traditional algorithms (SVM, RF, KNN, NB), artificial neural network (ANN), and traditional quantum neural network (QNN). Results demonstrate that the S-QNN model outperforms the optimal traditional algorithm by 5.67%, 6.19%, and 13.34% in the respective cases, and surpasses the QNN by 3.11%, 4.99%, and 3.84%. The S-QNN model exhibits robustness and versatility, highlighting its superiority in data processing. This study underscores the potential of quantum machine learning algorithms in geoscience research, showcasing the advantages of S-QNN and paving the way for innovative integration of quantum science and geoscience.

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Machine learning: A new approach to intelligent exploration of seafloor mineral resources

LIU Yang, LI Sanzhong, ZHONG Shihua, GUO Guanghui, LIU Jiaqing, NIU Jinghui, XUE Zimeng, ZHOU Jianping, DONG Hao, SUO Yanhui

2024, 31(3): 520-529.
DOI: 10.13745/j.esf.sf.2023.5.90

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The seafloor is characterized by abundant key mineral resources, which is a hotspot of current research and a new field of industry in the future. With the continuous progress of ocean exploration technology, the volume and dimensions of data from seafloor mineral exploration have increased dramatically, which has brought great difficulties and challenges to data processing and interpretation. In the face of massive data, traditional data interpretation and analysis methods expose many problems. Machine learning, with its strong self-learning ability, provides a series of intelligent analysis and decision-making solutions for unsolvable or difficult problems, improving the efficiency of data analysis. It is a new way for the intelligent exploration of subsea mineral resources. In recent years, machine learning has obtained extensive attention and research in the field of geosciences. Therefore, focusing on the application of machine learning to seafloor resource exploration technology, this paper firstly briefly introduces the classical model algorithms in machine learning; then elaborates on the application status of machine learning in two aspects of seafloor energy resources and metal mineral, and finally summarizes the application prospects of machine learning in the field of intelligent exploration of seafloor minerals, points out the problems in existing research, and proposes solutions and future development directions.

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Contribution ratio and distribution patterns of multiple oil sources in the Yanchang Formation of the Ordos Basin: A study utilizing machine learning and interpretability techniques

SU Kaiming, XU Yaohui, XU Wanglin, ZHANG Yueqiao, BAI Bin, LI Yang, YAN Gang

2024, 31(3): 530-540.
DOI: 10.13745/j.esf.sf.2023.9.56

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The Yanchang Formation within the Ordos Basin hosts multiple sets of potential source rocks, all exhibiting similar biomarker properties. The conventional method of oil-source correlation has proven ineffective, leading to longstanding debates within the field. In response to these challenges, this study introduces a novel deep learning-based scheme for oil-source comparison, leveraging artificial intelligence methods for research in this domain. The study presents the following key findings and insights: (1) Development of a deep neural network model for identifying the oil source type of unknown samples by utilizing 42 biomarker parameters from a diverse set of mudstone and shale samples representing different oil groups within the Yanchang Formation as training data. The model achieved identification accuracies of 83.0% for Chang 7 mudstone and 79.6% for Chang 8-Chang 10 mudstone, successfully distinguishing the primary source rocks of the Yanchang Formation from hydrocarbon generation products. (2) Application of the model to analyze the oil source classification of numerous sandstone and oil samples. The study calculated the contribution ratios of various source rocks to each oil group within the Yanchang Formation, summarizing their distribution patterns. (3) Conducting sensitivity analysis of the model using the permutation feature importance (PFI) algorithm, revealing differences in biomarkers between the two main source rocks of the Yanchang Formation. These findings contribute to advancing artificial intelligence techniques and technologies in the field of petroleum molecular geochemistry, offering valuable insights for future research and applications.

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