Table of Content

22 December 2020, Volume 34 Issue 06

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Petroleum Geology

Segmented Deformation and Activity Characteristics of the Tangbei Fault Zone in the Tarim Basin

YU Yixin, ZHANG Liwei, ZHU Xiuxiang, LUO Ji, LIU Shilin, ZHANG Zhongpei, JIN Feng

2020, 34(06):  1103-1109.  DOI: 10.19657/j.geoscience.1000-8527.2020.083

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The Tangbei fault zone is located in the northern Tangguzibasi sag, and has superimposing deformation features of segmented deformation and multi-stage activities. Based on defined interpretation of seismic profiles using fault-related fold theory and drilling data, this paper addresses the segmented deformation and activity characteristics of the Tangbei fault zone. The results show that detachment thrust faults and basement-involved thrust faults with fault propagation folds on hangingwall are well developed in the Tangbei fault zone. According to the shapes and deformation intensity, the Tangbei fault zone can be divided into three segments along strike, i.e.the western, central and eastern segments. From west to east, the deformation intensity and thrust angle decrease gradually. The Tangbei fault zone experienced four major tectonic activities in the Early Caledonian, the Middle Caledonian (phase I and III), and the Lately Caledonian-Early Hercynian. During the Early Caledonian and Middle Caledonian (phase I), the middle segment was highly active, and the seismic center gradually shifted westward. The multi-stage activities of the Tangbei fault zone are crucial for the formation of trap and, reservoir properties, as well as hydrocarbon migration.

Structure and Evolution Analyses of the Liaobei Area of Bohai Bay Basin

ZHANG Jiangtao, GUO Tao, WANG Bingjie, LI Honglin, WANG Maozhen

2020, 34(06):  1110-1118.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.082

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Based on fine interpretations of 3D seismic data and drill-hole data from northern Liaoning, the structural characteristics and fracture system of the basin are characterized in detail, and integrated with the regional geodynamic framework of the northern Liaodong Bay (northern part of the Liaoxi, Yuanyanggou, and central depressions). Cenozoic tectonic evolution process of the southern tip of the bulge and the northern tip of the Liaoxi bulge was analyzed in detail. The results show that: (1) Changes in the occurrence and activity of the major controlling basinal faults make the basinal structure in northern Liaoning different from south to north along the depression axis: the northern part is characterized by the southeast fault (sag). The simple half-graben fault features are controlled by the Liaoxi No.2 and No.3 faults in the middle, and two half-grabens are developed to form a domino-type half-graben system. The southern Liaoning large fault cuts the western boundary of the basin, as manifested by an asymmetric complex graben structure. (2) Paleocene-Eocene fault system has mainly NE-trending normal faults, which controls the basin basement structure. In the Oligocene, the NNE-trending strike-slip faults and their secondary faults dominate, and the main strike-slip fault zone has developed a typical trans-tensional/-pressive transition structure. The Neogene fault system is characterized by a series of secondary fault combinations with an NNE en echelon pattern. (3) Cenozoic northern Liaoning experienced three stages of tectonic evolution, i.e.Paleocene-Miocene strong extension and weak strike-slip stage, Oligocene strong extensional strike-slip stage, and Neogene strike-slip stage.

Characteristics About Hydrocarbon Accumulation Controlled by Structure in Paleogene of Dongpu Sag

YU Haibo, CHENG Xiushen, XU Tianwu, TAN Yuming, QI Jiafu

2020, 34(06):  1119-1131.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.081

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This paper analyzes the structure and structural style of Dongpu sag basin, and concludes that the Paleogene basin of Dongpu sag has the structural characteristics of multi-fault, multi-convex and multi-sub-sag.The multi-convex and multi-sub-sag basin structure controls the sub-sag and the hydrocarbon, and forms the multi-convex and multi-sub-sag and multi-reservoir migration unit. The sedimentary period of the upper sub-member of the fourth member and the lower sub-member of the third member of Shahejie Formation is the early-strong fault depression period, and the transition from single fault wide basin to strong fault deep basin, with a humid climate, wide lake basin and deep water body, is a strong reduction environment, and the quality of hydrocarbon source rocks is excellent. The sedimentary period of the middle and upper sub-member of the third member of Shahejie Formation is more faulted period, with the lake basin becoming slow, highly segmented and medium water body. The hydrocarbon source rocks are concentrated and of general quality in the center of each depression.The sedimentary period of the second member of Shahejie Formation is a weak faulted period, with a continuous multi-depression pattern and an independent hydrocarbon generating unit at the beginning of accumulation. The source rocks are not developed in a dry climate, a small lake-shallow water type, and a shallow water body. In the eastern sag belt of the basin, the area with a large buried depth of the upper and lower sub-member of the forth member of Shahejie Formation enters the threshold of hydrocarbon generation, and the source rocks mature rapidly. During the Dongying movement, the reservoir is mainly regulated, and the oil and gas generated in the early stage is transformed by small faults to form many small fault blocks. From late sedimentary period of Minghuazheng Formation to present, the fault activity is weakened, the formation thickness compensation in the sag zone continues to generate hydrocarbon, and the hydrocarbon accumulation is mainly in the lower part.

Sedimentary Characteristics and Mode of the Paleogene Funing Formation (3^rd Member) in the Subei Basin

WANG Xuying, JIANG Zaixing

2020, 34(06):  1132-1143.  DOI: 10.19657/j.geoscience.1000-8527.2020.084

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By analyzing the lithological composition, sedimentary structure, grain-size characteristics, single sand body thickness, logging response, and seismic reflection, the sedimentary system types of the Funing Formation (3^rd Member) in the Subei Basin are re-examined. The study concludes that river-dominated delta, wave-dominated delta and beach-bar systems, as well as storm depositional and nearshore subaqueous fan systems are developed in the study area. South winds prevailed during the stage of Funing Formation (3^rd Member) in the Subei Basin. The Western Jinhu and Yancheng sags are located on the leeward side, and are dominated by large-scale river-dominated delta system, where the wave effect is weak and the river effect is strong. The southern side of Jianhu uplift (Northern Gaoyou, Eastern Jinhu, and Hai’an sags) and the southern side of Binhai uplift (Suining and Yubei sags) are located in the windward gentle slope belt, and are dominated by wave-dominated delta and beach-bar systems. In these areas, wave action is strong, and lake waves and coastal currents may have transported and redistributed the deltaic front sand bodies. In the semi-deep lake areas of the Jinhu, Gaoyou and Haian sags, storm surges may have carried sediments from the shallow lake to the semi-deep lake environment, and developed a storm deposition system. The Southern Gaoyou Sag is located in the steep slope zone belt, and exhibits paleogeographic features of large terrain difference, near source and deep water, which is conducive to nearshore subaqueous fan system development.

Geochemical Characteristics and Controlling Factors of Organic Matter Enrichment of Wufeng Formation Shale in ZY3 Well, Northwestern Hunan Province

LIN Donglin, TANG Shuheng, XI Zhaodong, ZHANG Songhang, ZHOU Shulin

2020, 34(06):  1144-1152.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.085

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Based on the analyses on graptolite, lithological characteristics, GR curve and TOC content in the Wufeng Formation (Fm.) shale in ZY3 well in northwestern Hunan, the study area clearly belongs to the sedimentary period of WF2-WF3 shale graptolite belt. 20 samples from the WF2-WF3 in ZY3 well were selected to measure their trace elements and organic carbon isotopes compositions, and their vertical variation trends to reveal the controlling factors of organic matter enrichment in the Wufeng Fm. shale in northwestern Hunan were analyzed. The results showed that the organic carbon content in the shale was lower in WF2 (0.17% to 0.86%) and higher in WF3 (0.57% to 2.28%). The V/Cr, Ni/Co, V/(V+Ni) and U/Th values indicate that WF2 and the late-stage of WF3 were suboxic, whereas the early-stage of WF3 was anoxic. The P/Al value and Ba_xs content in shale indicate that WF2 and WF3 have relatively high paleoproductivity. However, the weak correlation between TOC and P/Al values and Ba_xs content, and the strong positive TOC vs. redox environmental index correlation indicate that the organic matter enrichment is mainly controlled by redox environment. Cerium anomaly and Mo/TOC values indicate the effects of frequent sea-level fluctuations and restricted basins on the paleoredox environment of the Wufeng Formation. Due to the sea-level rise in the early-stage of back bulge basin, WF2 may have formed in a sub-oxic environment. The coupling of sea-level rise and confined retention basin in the early-stage of WF3 resulted in hypoxia in the bottom water. In the late-stage of WF3, relative sea-level dropped due to the elevation peak of the Hunan-Hubei underwater upland, resulting in a sub-oxic environment that was not permissive to organic matter preservation. The results show that the redox environment was controlled by tectonic activity and paleo-sea-level change, which further affected organic matter accumulation in the Wufeng Fm. shale.

Geochemical Features and Geological Significance of Sandstone-type Uranium Deposit in Zhenyuan Area, Southwestern Ordos Basin

HU Yan, HU Yongxing, ZHANG Xiang, YANG Tao, OU Yangjian

2020, 34(06):  1153-1165.  DOI: 10.19657/j.geoscience.1000-8527.2020.086

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This study presents major and trace element data of the uranium-bearing Lower Cretaceous Luohe Formation (Fm.) sandstones in Zhenyuan area (southwestern margin of the Ordos Basin), and the metallogenic conditions and regularity.The results show that the uranium ores in the Luohe Formation is mainly uraninite (UO₂), and the uranium-bearing sandstone may have sourced from the quartzite in ancient sedimentary terranes or craton/recycled orogenic belts.These sandstones have the same REE patterns with LREE-enrichments, HREE depletions and negative Eu anomalies, suggesting that the wallrocks have a uniform detrital source, sedimentary environment and tectonic setting.The V/Cr, Ni/Co, U/Th and V/(V+Ni) features of the uranium-bearing sandstone indicate that the local uranium mineralization was mainly developed in a weakly-oxidizing to weakly-reducing transitional environment.The δEu and δCe values increase with the U content, reflecting that the U enrichment and mineralization have experienced the transformation from oxidizing to reducing environment, and the sand body colors have changed from light red to grayish white.The contents of Th, Sc, Co, Mo in the uranium-bearing sandstones are positively correlated with that of U, and thus the former four elements can be used as fertility indicators for sandstone-type uranium deposits in the Luohe Formation.Formation of sandstone-type uranium deposits in the study area is closely related to the reduction caused by the upward seeping of oil and gas from depth.The incursion of oil and gas fluids likely increases the reducing capacity of the sand body, which promotes the uranium deposition and concentration from the oxidizing uranium-bearing fluid in the redox transition zone.This eventually formed the widespread uranium anomalies in the Luohe Formation.

Pressure Evolution of Upper Paleozoic in Hangjinqi Area, Ordos Basin

WANG Huan, MA Liyuan, LUO Qingqing, CHEN Chunfang, HAN Bo, LI Chao, ZHENG Xiaowei

2020, 34(06):  1166-1180.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.080

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Evolution of abnormal pressure was quantitatively determined by basin numerical simulation system, based on the analyses of current reservoir pressure, disequilibrium compaction and inclusion paleo-pressure of the Upper Paleozoic in Hangjinqi area, Ordos Basin. The study shows that current pressure in the reservoir is of under-pressure, whose coefficient decreases gradually from south to north. The target zone is the deepest by the end Early Cretaceous, meanwhile, the maximum over-pressuring of mudstone is concentrated in the lower Upper Shihezi Formation to the third member of lower Shihezi Formation. The maximum over-pressuring in mudstone varies in different zones. The maximum over-pressuring is of 15 to 20 MPa (locally >20 MPa) in west of Hangjinqi, medium over-pressuring occurs in the east between 10 MPa and 15 MPa, while the minimum over-pressuring (5 to 10 MPa) occurs in the north. The numerical simulation results show that the evolution of abnormal pressure is syn-tectonic. Residual pressure (RP) of the Upper Shihezi Formation began to form in the end Triassic under the Indosinian orogenic influence with a maximum of >10 MPa. During the Middle Jurassic, the RP decreased slightly under the influence of the early Yanshanian Movement. During the Cretaceous, the RP was mostly affected by late Yanshanian Movement with >20 MPa. Subsequently, the RP decreased rapidly with the structural uplift and denudation, and abnormally low pressures in the current reservoirs and partly residual pressures in caprocks were formed. The main factors for the formation of under-pressuring in Hangjinqi area are the gas diffusion, temperature drop and tectonic unloading caused by uplifting and denudation. The paleo-pressure genesis varies between different source rocks, caprocks and reservoirs. Generation of organic materials in the source rocks is the main factor for the RP formation, while disequilibrium compaction plays an important role in caprocks. The configuration of sand and mudstone is essential in the paleo-pressure formation in reservoirs. The third member of the Xiashihezi Formation is mainly composed of sandstone surrounded by thick mudstone, which is greatly affected by disequilibrium compaction. The lower part is composed by mudstone-sandstone interbeds or mudstone surrounded by thick sandstone. Effect of the disequilibrium compaction is weakened or even disappeared, and structural extrusion is a dominant control for reservoir paleo-pressure.

Karst Reservoir Type, Cave Structure and Genetic Model of Ordovician Tahe Reservoirs: Case Study of Fracture-cavity Unit T615 in Tahe Oilfield 7 Block

XU Jiahong, KANG Zhihong, LAN Xixi

2020, 34(06):  1181-1192.  DOI: 10.19657/j.geoscience.1000-8527.2020.087

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The Ordovician Tahe carbonate reservoirs are dominated by karst fractures and caves. With the advance of oilfield development and geophysical surveying technology, the morphology of karst underground rivers has become clearer. However, due to the complex spatial structure, karst products and the types of reservoirs, structures and development patterns of karst reservoirs differ greatly. Take the fracture-cavity unit T615 as an example, we used high-resolution seismic data, together with core logging, FMI imaging logging, and single-well performance data, the reservoirs in the well area are divided into four types, i.e.filling (sand-mudstone filling and fine sandstone filling), collapsed-breccia filling, karst cave (unfilled) and dissolution crack types. Combined with the collected high-resolution 3D seismic attribute characterization data, the distribution characteristics and identification marks of the major products (hall cave, main stream cave, terminal cave, falling water cave and resident water cave) of typical karst systems are studied, and the karst formation is divided into 4 periods. After structural and filling reconstruction, different cave structures, karst products and reservoir types are found in the four-layer cave. Integrating hydrogeology and karst theory, the geological profile of the continuous well karst fractures and caves, and their genetic model in a typical karst system are established. This reveals the combination of fractures and caves between wells, and provides guidance for the description and characterization of karst reservoirs.

Diagenesis and Porosity Evolution of Calcareous Sandstone Reservoirs of Xu-3 Member in Western Yuanba of Northeastern Sichuan Basin, China

WANG Ai, ZHONG Dakang, LIU Zhongqun, WANG Wei, DU Hongquan, ZHOU Zhiheng, TANG Zicheng

2020, 34(06):  1193-1204.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.079

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Based on data of thin-section micropetrography, scanning electron microscopy (SEM) and physical property test, we analyzed the petrological characteristics, diagenesis, pore type and physical properties of the tight sandstone of Xu-3 Member in the western Yuanba area (northeastern Sichuan Basin). We established its diagenetic sequence and pore evolution process, which can shed light on the exploration of the Xu-3 Member tight sandstone. We show that the Xu-3 Member tight sandstone is mainly provided by the parent rocks of Longmenshan Permian and Triassic carbonate rocks, and was mainly developed in the braided river delta plain-deltaic front of medium-fine grained calcareous sandstone. Diagenesis of these sandstones includes mainly compaction and pressure dissolution, calcite cementation, recrystallization, dissolution and fracturing. The pore types include intercrystalline micropores, cracks and dissolved pores, with the porosity of 0.41% to 7.16% and permeability of 0.001,2×10^-3 to 533.59×10^-3 μm². The uniquely high-Ca content of the calcareous sandstone may have formed the typical diagenetic characteristics of strong cementation and recrystallization, but weak compaction and dissolution. The unique burial diagenesis has formed the special pores and physical properties of the calcareous sandstone. Early intensive calcite cementation may have resulted in weak compaction of calcareous sandstone, almost loss of primary pores, and weak dissolution. In the later stage, recrystallization of the muddy algae sands in the calcite chips formed many intercrystalline micropores. Average porosity of the calcareous sandstone is only 2.0%, and the physical properties are poor. The detrital particles and cement of the calcareous sandstone are mainly carbonate minerals with brittle characteristics. Under tectonic movements, cracks are readily formed which connected the pore system to communicate a large number of recrystallized micropores, intergranular dissolved pores, and residual intergranular pores.

Quantitative Characterization of Rock Microstructure of Digital Core Based on CT Scanning

ZHAO Jianpeng, CUI Likai, CHEN Hui, LI Ning, WANG Ziliang, MA Yao, DU Guichao

2020, 34(06):  1205-1213.  DOI: 10.19657/j.geoscience.1000-8527.2020.044

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Rock microstructure is a key parameter that determines the macro-physical reservoir properties. CT core scanning technology can perform three-dimensional (3D) visualization and fine quantitative characterization of rock microstructures. In this paper, rock cores of the Huagang Formation (Fm.) from north of the central inversion zone of the Xihu Sag (East China Sea Basin) are used as an example. Firstly, 3D digital core images were established by CT scanning. Secondly, the image processing algorithm and the “maximum ball” algorithm were used to analyze the samples. The grain size distribution and pore structure are spatially and quantitatively analyzed. The Huagang Fm. rock grain size is mainly 100-300 μm, belonging to fine sandstone. Different grain sizes lead to differences in pore structure, and the reservoir pore connectivity and structural parameters are quite different. Non-connected pores are mainly isolated. The pore radius ranges mainly 20-60 μm, whilst the throat radius and length is 3-15 μm and 15-45 μm, respectively. The pore-throat coordination numbers are quite different (mostly from 0 to 4), and the pores and throats are largely triangular. This study enhances the quantitative evaluation of reservoir micro-parameters, and provides strong technical support for visualizing and quantitative characterizing rock microstructures.

Comprehensive Classification Scheme of Huagang Reservoir in Xihu Depression

WANG Meng, LIU Zhijie, YANG Yuqing, ZHANG Zhiqiang, LIU Haibo, DONG Yu

2020, 34(06):  1214-1220.  DOI: 10.19657/j.geoscience.1000-8527.2020.060

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This paper presents the lithology, physical properties, and pore structure of the Huagang reservoir based on a large experimental dataset of thin-section, granularity, mercury injection and gas-water phase permeability. The study shows that lithology of the Huagang Formation is dominated by fine sandstone with diverse pore types and poor pore structure, which constitutes a (ultra-)low-permeability reservoir. Based on the reservoir features, we focus on the use of reservoir dynamic permeability and flow unit index to categorize the reservoir capacity. Seven types of reservoir parameters are selected, and the reservoirs are divided into four categories, including Class I and II (with natural production capacity), Class III (need to be fractured), and Class IV (ineffective reservoir). Practical application shows that the Huagang reservoir classification scheme proposed is consistent with the actual test results, and has good application potential.

Application of X-ray Computed Tomography in Biogenic Structure Identification

WANG Yuanyuan, WANG Cui, WANG Xueqin, HU Bin, WANG Changzheng

2020, 34(06):  1221-1229.  DOI: 10.19657/j.geoscience.1000-8527.2020.078

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X-ray Computed Tomography provides realistic basis for the interpretation of the morphology, structure, taphonomy and related environmental characteristics of the biogenic sedimentary structures. X-ray Computed Tomography can assist non-sample-destructive reconstruction the internal structure, and generates high-resolution three-dimensional (3D) bioglyph images. The technique can enhance the analyze of the morphological and structural characteristics of biogenic sedimentary structures. This technoque can then be used to study biological behaviors, ecological habits and the analogy of trace fossils. Meanwhile, it supports the identification and morphological classification and ecological classification of trace fossils, which provides a more accurate indication of the reconstruction of paleogeographic and palaeoecological environment. In addition, the undefined trace fossils left by conventional analytical techniques could be re-analyzed. The application of X-ray computed tomography in biogenic structure identification will produce new understanding and new ideas. It will also promote the X-ray computed tomography in ichnological applications.

Petrology

Petrogenesis and Tectonic Significance of the Wuzhangshan Pluton in Xiong’ershan, Western Henan Province: Constraint from Petrogeochemistry and Sr-Nd-Pb Isotopes

RAO Shicheng, WANG Changming, HE Xinyu, SHI Kangxing, ZHU Jiaxuan, CHEN Qi, DUAN Hongyu, LI Pengwei

2020, 34(06):  1230-1244.  DOI: 10.19657/j.geoscience.1000-8527.2020.043

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To analyze the magma origin and mechanism of the Yanshanian magmatism in eastern China, the authors conducted a study on the petrography, Sr-Nd-Hf isotope systematics, whole-rock major and trace element geochemistry of the Wuzhangshan pluton in Xiong’ershan. The Wuzhangshan pluton consists of biotite hornblende monzogranite, which is characterized by high SiO₂(66.44%-71.71%) and alkali contents (Na₂O+K₂O=9.8%-10.06%). The rocks contain relative high Al₂O₃(14.52%-15.63%), and low TFeO (1.71%-3.47%), CaO (0.51%-2.56%) and MgO (0.19%-0.59%), indicating their shoshonitic and metaluminous nature. The samples are enriched in LREEs, K, Sr, Pb, Zr, and Hf, but depleted in high field strength elements (HFSEs) such as HREEs, Ta, Nb, P,and Ti. These rocks have no obvious Eu anomaly (δEu=1.00-1.13) and with I-type granite characteristics. They have (⁸⁷Sr/⁸⁶Sr)_i=0.707,3 to 0.708,0, ε_Nd(t)=-20.5 to -17.9, and T_{\mathrm{D}{\mathrm{M}}_2} =2,599 to 2,389 Ma. Lead isotope compositions are similar (²⁰⁶Pb/²⁰⁴Pb=17.305-17.754; ²⁰⁷Pb/²⁰⁴Pb = 15.427-15.481; ²⁰⁸Pb/²⁰⁴Pb = 37.766-37.999), indicating that rocks were sourced from ancient crust material. These rocks have high values of Sr/Y (40.85-236.72) and La/Yb (19.34-30.46), indicating adakite-like features. The low MgO, Cr, and Ni contents and low Mg^# values indicate that the monzogranite was formed by partial melting of the thickened lower crust, probably related to the north-dipping intracontinental subduction of the Yangtze plate.

Zircon U-Pb Ages, Geochemical Characteristics and Tectonic Implications of the Riduoma Granodiorite in the Middle Section of Western Qinling Orogen

KOU Shaolei, WEI Liyong, ZHANG Zhen, LI Guoying, ZHENG Xin, LU Zongyue, YANG Hanwen, MENG Wuyi

2020, 34(06):  1245-1260.  DOI: 10.19657/j.geoscience.1000-8527.2020.029

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Riduoma granodiorite is located near the Meiwu pluton in the middle section of the Western Qinling Orogen. A integrated study of petrography, U-Pb zircon dating and whole-rock geochemistry was carried out for the Riduoma granodiorite. The granodiorite contains numerous mafic microgranular enclaves (MMEs). LA-ICP-MS zircon U-Pb dating yielded a weighted mean age of (236.8 ± 3.6) Ma (MSWD=4.1) for the granodiorite and (242.7±1.6) Ma (MSWD=1.4) for the MMEs. The Riduoma pluton is weakly peraluminous (A/CNK=1.48-1.51) and high-K calc-alkaline, with high contents of K₂O (2.58%-2.75%), K₂O+Na₂O (5.57%-5.76%), and belongs to I-type. The granodiorite is characterized by enrichment in LILEs (such as K, Rb, Ba, Th, and U) and depletion in HFSEs (such as Nb, Ta, Ti and P) with high LREE/HREE ratios (10.4-11.9) and moderately-negative Eu anomalies (δEu=0.68-0.81). Geochemical characteristics of the Riduoma granodiorite suggest that it was derived from partial melting of the lower crust high-K basaltic rocks. In addition, the granodiorite shows relatively high Mg ^# (57-61), Cr (149×10^-6-185×10^-6), and Ni (36×10^-6-47×10^-6), suggesting minor mantle-derived contribution. The MMEs may represent this source magma. Petrography, zircon U-Pb ages, and geochemical characteristics, combined with the regional setting, suggest that the Riduoma pluton emplacement was resulted from the subducted slab break-off in a post-collisional setting.

Igneous Assemblage and Metallogenic Background of the Mawu Gold Deposit in the Min-Li Ore Belt of the Western Qinling Orogen

GUO Na, LIU Cui, CUI Long, YAO Wei, LI Guoying, GAN Liming, HUANG Yong

2020, 34(06):  1261-1276.  DOI: 10.19657/j.geoscience.1000-8527.2020.072

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The Mawu gold deposit in Gansu Province is a medium-sized finely-disseminated gold deposit, which is located in the eastern part of the Min-Li ore belt in the Western Qinling Orogen, and in the exocontact of the Zhongchuan intrusion. A series of analyses on the fieldwork geology, petrology, geochronology, and geochemistry of the igneous rocks from the mining area were carried out to reveal the ore-causative igneous rock assemblages and their characteristics, and to explore their petrogenetic and geotectonic background as well as gold ore formation. Field observations indicate that the lamprophyre dikes/veins, aplitic dikes, and quartz diorite dikes were developed near or crosscut the gold veins, indicating that the gold ores and magmatic dikes were nearly coeval. LA-MC-ICP-MS zircon U-Pb dating of the lamprophyre and granitic dikes indicates that they were formed at about (153.5±3.5) Ma to (154.9±0.9) Ma, suggesting a Late Jurassic gold mineralization. Therefore, the work concludes that the igneous assemblage of Mawu gold deposit are dominated by dikes. The dikes have a wide composition range of SiO₂, K₂O, Na₂O, TFeO and MgO, belonging to different igneous types and likely derived from different magma sources. The occurrence of wide spectrum dike swarm (WSDS) means that it was formed under an extensional environment caused by lithospheric delamination of the orogen. The dikes and gold orebodies intruded into the Zhongchuan granitic rocks and other wall-rocks, which indicates that they were formed after large-scale magmatic activities and batholith uplift in the late Western Qinling orogeny, and belongs to post-batholith metallogeny.

Geochronology, Petrogenesis and Geological Significance of the Puquan Granite Pluton in Dayaoshan Area, Guangxi

CHEN Huan, KANG Zhiqiang, WU Jiachang, LI Daixian, CAO Yan, WEI Tianwei, WEI Naishao, LIU Di, ZHOU Tong, LIU Dongmei, LAN Haiyang

2020, 34(06):  1277-1290.  DOI: 10.19657/j.geoscience.1000-8527.2020.046

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Caledonian magmatic rocks are widespread in the Dayaoshan uplift zone in Guangxi Province, and research on them has instructional significance for understanding the geodynamic setting, evolution mechanism and prospecting work of Dayaoshan uplift. This paper present the first detailed geochronological, elemental and Hf isotope study on the Puquan intrusion in the northwestern uplift zone. LA-ICP-MS zircon U-Pb dating on the Puquan intrusion yielded Late Ordovician age of (441.1±1.2) Ma (MSWD=0.14). The intrusion comprises medium-fine-grained I-type granite, and is characterized by high SiO₂ (68.50%-72.83%) and medium Al₂O₃ (13.66%-14.42%) contents and medium alkalinity (total alkali=7.17%-8.34%, K₂O/Na₂O=0.75-1.33) with A/CNK=0.89-1.18, suggesting its metaluminous to weakly peraluminous nature. The rocks are enriched in LILEs (such as Rb, Th, U, and Pb) and depleted in Ba, Sr, Nb, and Ti. The total REE contents are 97.41×10^-6-178.80×10^-6, and the rocks have distinctly negative Eu anomalies (δEu=0.12-0.14). The magmatic zircon ε_Hf(t) values are mostly negative (-14.92 to 2.75), with an average of -2.67. In the ε_Hf(t) vs. age and the (¹⁷⁶Lu/¹⁷⁷Hf) vs. age diagrams, the samples fall below the chondrite evolution line, and the two-stage model ages ( t_{\mathrm{D}{\mathrm{M}}_2} ) are of 1.2 Ga to 2.4 Ga (average 1.6 Ga), indicating that the rocks may have derived from partial melting of the Mesoproterozoic crustal material with possible mantle-derived components. This shows that the Puquan intrusion was formed under syn-collisional compression between the Yangtze and Cathaysia Plate.

Ore Deposits

Characteristics of Structural Superimposed Halos and Deep Prospecting Prediction in Erdaogou Gold Deposit, Liaoning Province

WEN Jiawei, SHI Pengliang, LIU Yanbing, ZHANG Jing, QU Hailang, LI Yuanshen, HU Boxin, MIAO Guang

2020, 34(06):  1291-1302.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.17

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Erdaogou gold deposit in Liaoning Province is a magmatic-hydrothermal deposit hosted in continental volcanic rocks, orebodies are strictly controlled by structures. In order to study the characteristics of structural superimposed halos and predict the extension of No.1 and No.3 orebodies, this paper systematically studied the characteristic indicator elements, structural superimposed halos axial zoning sequences, anomaly threshold and geochemical parameters of the samples at the 450 m to -305 m depth. The results show that the indicator elements are Sb and Hg for front-ore halos, Au, Ag, Cu and Pb for near-ore halos, Co and Ni for late-ore halos, respectively. From top to bottom, the axial zoning of superimposed halos are Co→Sb→Cu→Au→Hg→Ni→Pb→Ag for No.1 orebody, Ag and Cu→Hg→Au→Pb→Sb→Co and Ni for No.3 orebody. These geochemical parameters indicate that the No.1 orebody was respectively superimposed at 370 m, 130 m, -215 m depth and the No.3 orebody was superimposed at -125 m, -215 m depth,based on this, we established the ideal models of structural superimposed halos. The anomaly characteristic map of structural superimposed halos shows that the anomaly intensity of front-ore halos and near-ore halos are large, while late-ore halos are small of No.1 orebody at -215 m depth. The anomaly intensity of front-ore halo, near-ore halo and late-ore halo of No.3 orebody are larger at -215 m depth. To sum up, we deduce that the No.1 orebody still has a great extension below -215 m depth, while the No.3 orebody has a certain extension deep down.

Geochemistry

Soil Geochemical Characteristics and Metallogenic Potential in Weibo Mountain Area of Ejina Banner, Inner Mongolia

HU Erhong, ZHANG Shanming, HE Zhongyin, ZHANG Hua, LIU Ruiqin, HU Yuchao, HE Shiming, LIU Ting, SUN Hao

2020, 34(06):  1303-1317.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.18

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Geochemical exploration is one of the quickest prospecting methods to discover prospective area and reduce the target area. Based on the 1∶50,000 soil geochemical survey, this paper studies the geochemical characteristics of 18 elements in Weibo mountain area, summarizes the distribution law of 18 elements. It is found that the anomalies of Rb, Nb, W, Mo, Bi, Au, Cu in the area are significant. Ten comprehensive ano-malies are delineated and the metallogenic potential of the main comprehensive anomalies is evaluated. It can be found that AP5(B2)comprehensive anomaly has geological-geochemical conditions for gold polymetallic deposit, AP6(B1)comprehensive anomaly has potential for large-scale Rb-Nb-Ta mineralization and AP8(B2)comprehensive anomaly has W-Mo-REE mineralization. For the anomaly verification, the gold ore (mineralization) bodies were found in AP5, and rare and rare earth elements ore (mineralization) bodies have been found in AP6 and AP8, which have great metallogenic potential. Among them, the discovery of granite pegmatite Nb-Ta-Rb and high temperature hydrothermal Mo-REE mineralization types is the first case in Beishan metallogenic belt, Inner Mongolia. Meanwhile, it also provides the basis for the change of prospecting ideas in this area.

Research of 1∶50,000 Land Quality Geochemical Assessment at Yanjin County in Yunnan Province

YANG Fan, ZHANG Shunyao, SONG Yuntao, WANG Huiyan, HAN Wei, GUO Zhijuan, PENG Min, WANG Chengwen, CHEN Ziwan, BAI Bing

2020, 34(06):  1318-1332.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.19

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Controlling the quality and quantity of land resources, development and utilization of special land resources, farmland protection and the management of ecological protection are very important in the construction of ecological civilization. A research on the assessment methods of 1∶50,000 land quality geochemical survey at Xinglong, Luoyan and Niuzhai of Yanjin county in Yunnan province was carried out. The soil samples were collected at a density of 9.17 samples/km². The distribution of nutritive elements and heavy metal elements, and the comprehensive quality of soil in the study area were studied. For delineating special land resources, the national standard of green food-environmental quality for production area and pollution-free agricultural products-environmental quality for production area were tentatively applied in this study. Research on farmland protection planning was carried out, according to the soil pollution controlling action program enacted by State Council of the People’s Republic of China. Results show that 72.88 percent of the study area and 69.17 percent of the cultivated land area are assessed above three-class as shown in the national standard of specification of land quality geochemical assessment. Selenium-enriched land with area of 191.73 km², that is accounting for 75.53 percent of the total study area,is discovered. Selenium-enriched farmland and garden plot with area of 66.84 km² are discovered, accounting for 70.92 percent of the total cultivated land and garden plot area in the study area. The farmland and garden plot that meet requirements of production area of the green food and pollution-free agricultural products are distinguished, and the area are 11.60 km² and 11.76 km², respectively. The farmland and garden plot are marked out as priority reserve area, security utilization area and strict control area, with the area of 65.57 km², 21.67 km², 7.00 km², and accounting for 69.59, 22.98 and 7.43 percent of the total farmland and garden plot area in the study area, respectively. These results could be used to the land resource management, agricultural structure adjustment, soil environmental protection and po-verty overcoming for the local government. It also could be used as a reference for improving the utilization degree and achievement transformation of land quality geochemical assessment results. It is of great significance to enrich and perfect the system of land quality geochemical assessment.

Water Resources and Environment

Analysis of Pollution Distribution Characteristics of Soil and Groundwater Around A Chemical Device

SUN Zhibin, HU Zhenguo, LIU Fei, YANG Xinmin, ZHAO Bei, JIANG Guoliang

2020, 34(06):  1333-1340.  DOI: 10.19657/j.geoscience.1000-8527.2020.06.20

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In this paper, a chemical device workshop in Jiangsu Province was selected as the investigation object. Soil and groundwater samples from different locations in the workshop were collected by drilling, and the types, concentration and distribution characteristics of pollutants in soil and groundwater were detected and analyzed. The results show that the soil and groundwater in the workshop are polluted to a certain extent: the concentration distribution of pollutants in the soil are closely related to the lithology, the lithologic soil layer with poor permeability often leads to accumulation of pollutants; due to the shallow groundwater level and the good permeability of soil lithology, pollutants are not easy to remain in the soil environment for a long time, but easy to migrate from the soil environment to the groundwater environment, resulting in more serious pollution in groundwater. The pollutants in the soil that exceed the standard are benzene and cobalt, which are mainly distributed in shallow miscellaneous fill and silt layer. Many pollutants in groundwater exceed the standard, including benzene, 4-chloroaniline, petroleum hydrocarbon, manganese, cadmium, lead, sulfate, fluoride and ammonia nitrogen. The relationship between the distribution characteristics of pollutants and the properties of pollutants, soil lithology was analyzed to provide the basis for site selection of chemical companies, and pollution prediction, prevention and control.