Table of Content

10 December 2018, Volume 32 Issue 06

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Petroleum Geology

Characteristics and Formation Mechanisms for the Saline Lacustrine Oil in the West Slope of the Dongpu Sag

LI Lei, LI Sumei, ZHANG Hongan, XU Tianwu, ZHANG Yunxian, JI Hong

2018, 32(06):  1109-1124.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.01

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The hydrocarbons generation and migration style in the West Slope of the Dongpu Sag is rather complex. Geochemical methods including GC/MS, ESI FT-ICR MS and isotopic analysis, combined with geological methods are used to reveal hydrocarbon characteristics and genetic mechanisms for the saline lacustrine oils. The crude oils analyzed were subdivided into two oil families. Oil family-I is these oils in the Mazhai Tectonic Belt, which were characterized by relatively low ratios of Pr/Ph (mean 0.39) and C₂₉-/C₃₀-hopane (mean 0.33), and relatively high ratios of C₃₅-/C₃₄-hopane (mean 1.56) as well as dibenzothiophene/phenanthrene (mean 0.27). This family was primarily derived from the Es₃^L-Es₄^U mudstones/shales deposited under strong reduction and saline-water paleoenvironment in the Mazhai Sag. Oil family-Ⅱ is those oils in the Huqing-Xingzhuang area, featured by characteristics of a little different from the family-I, which has a relatively low ratio of C₃₅-/C₃₄-hopane and dibenzothiophene/phenanthrene relative to the oil family-I. The oils of family-Ⅱ are primarily derived from the Es₃^L-Es₄^U mudstones/shales in the Huqing Tectonic Belt and the adjacent Haitongqi Subsag with a burial depth >3,000 m according to oil-source rock correlation. It is the precursors and paleoenvironment which caused the differences between the oils. Abundant sulfur compounds with relatively low thermal stability were detected in the deep oils analyzed by ESI FT-ICR MS, accompanied by relatively high sulfur isotope of individual sulfur compounds. Both of the phenomenon suggest thermochemical sulfate reduction (TSR) experienced by the oils. Two thermal evolution trends were observed for the source rocks in the area suggesting affection of thick gypsum-salt rocks on the hydrocarbons generation of the source rocks. Most of the crude oils in the Huqing area are less mature, which is not coincided with the considerable amounts of deep source rocks developed in the area, suggesting a good potential of deep tight oil-gas exploration and exploitation in the area.

Controlling Effects of Gypsum-salt on Hydrocarbon Generation of Source Rocks in Dongpu Sag and Its Significance on Petroleum Geology

CHEN Xiangfei, LI Sumei, ZHANG Hongan, XU Tianwu, ZHANG Yunxian, WAN Zhonghua, JI Hong, GUO Zhenqian

2018, 32(06):  1125-1136.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.02

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Gypsum-salt rocks were extensively developed in the northern part of the Dongpu Sag, Bohai bay Basin.The effects of gypsum-salt rocks on characteristics and hydrocarbon generation of source rocks are barely documented. Geological and geochemical methods were used to investigate such effects. Obvious differences were observed between the source rocks in the saline and non-saline areas of the sag. Dark grey and brown shales in the north saline area are recognized as excellent source rocks with TOC content over 1.5%, dominated by kerogen type Ⅱ₁ and Ⅰ of organic matter.Source rocks in the south fresh water lacustrine(non-saline area) were dominated by kerogen type Ⅱ-Ⅲ which is favourable for gas generation. This indicates that the property and hydrocarbon generation potential of the source rocks in the area are strongly controlled by gypsum-salt rocks.It was also observed that hydrocarbon generation process of the source rocks is strongly influenced by gypsum-salt rocks.Oil generation window would be expanded obviously when the thickness of gypsum salt is about 50 m.Both the oil and wet gas windows would be enlarged within a certain degree with increase of salt rocks’ thickness. The oil generation window would be narrowed when the thickness of salt rocks reached around 400 m,while wet gas window would be further enlarged. The effects of gypsum-salt rocks on oil and gas generation windows of the source rocks were ascribe to their high thermal conductivity, which could influence geothermal field. Hydrocarbon generation modes for potential source rocks in the saline and non-saline area were established based on a comprehensive study of geology and geochemistry. The models could have a great instructive significance to petroleum exploration in the Dongpu Sag and the similar salt bearing basins.

Organic Petrology of Mesozoic Source Rocks in the Northern Piedmont Zone of the Kuqa Depression

LIANG Wanle, LI Xianqing, WEI Qiang, LI Jin, SUN Kexin, ZHANG Min

2018, 32(06):  1137-1149.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.03

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Using whole-rock organic petrological analysis, the macerals, major hydrogen-rich components, organic matter types and thermal evolution of organic matter in the Triassic-Jurassic source rocks from the northern piedmont zone of the Kuqa depression are revealed. The results show that the total maceral content of the Jurassic Kezilenuer Formation source rocks is the highest in the northern piedmont zone, and that in the Qiakemake Formation source rocks is the lowest. The Mesozoic source rocks lack sapropelite, but are rich in vitrinite and relatively rich in exinite and inertinite. The maceral contents of these source rocks vary according to their respective formations.The vitrinite contents of the Kezilenuer and Qiakemake formations are relatively high, and exinite in the Qiakemake Formation is relatively well developed.It is suggested that sporinite, liptodetrinite, cutinite and alginate are the main hydrocarbon-forming macerals, and the hydrocarbon-forming maceral content in the Qiakemake Formation is the highest.Organic matter in the source rocks are mainly of Type Ⅲ and Ⅱ₂, which are beneficial for gas formation. Thermal evolution level in these source rocks are in the mature and high-mature stage,with the vitrinite reflectance (R_o) of 0.56% to 1.87%. The results show that the hydrocarbon-forming center locates in the thrusting front of the Kelasu thrust belt, with the highest total maceral content and thermal evolution. High oil-forming potential of hydrocarbon source rock is related to high proportion of liptinite macerals and low content of terrigenous organic matter.

Hydrocarbon Distribution Pattern of Superimposed Unconformity Structure: A Case of Carboniferous Donghe Sandstone in Tazhong Area, Tarim Basin, NW China

WANG Tao, XU Huaimin, DENG Xili, DONG Shaoqun, JIANG Tongwen, ZHOU Xinping, HUANG Ya

2018, 32(06):  1150-1160.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.04

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In this paper, we discuss: (1) the unconformity types along the Donghe sandstone third-order sequence boundary; (2) different ways of hydrocarbon migration and accumulation caused by space-time orderly distribution of unconformity structures. The Donghe sandstone can be divided into superstratum of the unconformity (bottom), in-place carrier bed, residual regolith, weathered clay bed, superstratum of unconformity (top) and regional cap rock. Pool-forming units are different in the northwest and southeast of the district. They can form 2 groups and 7 types of pool-forming structures, with the former corresponding to two groups of reservoirs. Major structures are separated in the northwest. Hydrocarbon can migrate below the weathered clay bed and regional cap rock, forming the unconformity-blocked reservoir group, including anticlinal reservoir of superstratum of unconformity (top), lithologic reservoirs of superstratum of unconformity (top) and low amplitude anticlinal reservoir of residual regolith. Structures are connected in the southeast, and the hydrocarbon may have migrated below the superstratum of unconformity (bottom) and regional cap rock, forming the unconformity-connected reservoir group, including connected anticlinal- and connected stratigraphic overlap reservoirs. This finding facilitates further hydrocarbon exploration in the Donghe sandstone.

Source-to-sink System and Reservoir Property Variation of the Second Member of Liushagang Formation in the Southern Steep Slope, Wushi Sag

HE Weijun, XU Wanxing, LIU Juan, LIU Fang, JIAO Xiangyan

2018, 32(06):  1161-1172.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.05

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In recent years, the southern steep slope of the Wushi Sag has become an important oil-gas exploration target in the Beibuwan Basin, in which the second member of the Liushagang Formation is considered as the main target layer. To identify the distribution pattern of sand and favorable reservoirs, we conducted detailed source-to-sink and fracture system analyses, discussed the coupled fracture-provenance deposition controls and the main factors of favorable reservoir distribution, based on comprehensive analyses of drilling and seismic data. The results reveal an obvious lake retreat in the middle bed of the Liushagang Formation second member, which developed a fan delta system. The slope-break and F7 fault zone likely controlled the development of medium-large fan delta systems in this area, and we have summarized three types of structurally deposition control patterns. Parent lithologic differences are likely the main cause for the reservoir dissolution. The main parent rock type in the central and western districts is magnetite granite. Its sediments contain less stable minerals such as K-feldspar, which formed dissolved pores and improved the physical properties of the reservoir. The above analysis shows that the central and western districts are favorable exploration areas due to the large fan delta development and good reservoir physical properties.

Stratigraphy of the Cambrian Subsalt Metamorphic Rocks in the Tanggu Depression (Well YL6) and Its Petroleum Geological Significance

FU Xiaotao, WANG Bin, WANG Xiang, WANG Xiaoming, QU Yang, REN Ping, ZHOU Haodong, LI Xiangyun

2018, 32(06):  1173-1181.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.06

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Thick layers of Cambrian dolomite with favorable petroleum geological conditions and great exploration potential are widely developed in the inter-platform basin of the Tarim Basin. However, the rocks under middle Cambrian in well YL6 are marble instead of dolomite, and their age determines whether the paleo-land extended to the Madong tectonic belt in the Early Cambrian. By analyzing the drill cores, slices, SEM data, fossils, logging and seismic data, we identified the petrological characteristics and formation of the marble in well YL6. We concluded that: (1) Distribution of the marble in well YL6 is transitional, and the metamorphic minerals in the marble indicate that the marble in well YL6 was formed by local thermal metamorphism instead of regional metamorphism; (2) Fossils and seismic data indicate that the Lower Cambrian dolomite is widely distributed in Madong area, and that the metamorphism occurred along deep faults which are locally distributed in this area;(3) The Lower Cambrian sequences in the Madong area have favorable petroleum geological conditions and exploration potential for discovering primary reservoirs and structural-lithologic reservoirs.

Characteristics of Micro-pore Structure and Differential Analysis of Logging Identification for Different Diagenetic Facies in Low Permeability Reservoir:A Case Study on Chang 6₁ Reservoir in Wangpanshan Area of Jiyuan Oilfield

HAN Jin, SUN Wei, YANG Bo, FAN Xiujiang, WU Yanjun

2018, 32(06):  1182-1193.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.07

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Based on information from casting thin sections, scanning electron microscopy (SEM), core photos and constant speed mercury pressure analysis, and with the consideration of the material source, clay mineral, pore type and diagenesis, the Chang 6₁ reservoir of Wangpanshan is divided into six different diagenetic facies. The dominant reservoir facies are kaolinite+chlorite cementation-intergranular pore, kaolinite cementation-dissolved pore+intergranular pore, and chlorite+kaolinite cementation-dissolution pore. This study shows that the microscopic pore structures and logging responses of the different diagenetic facies are various. The variation of micro-pore throat in each diagenetic phase is distinct, especially in the capillary pressure curve and throat. Correlation between the throat radius and permeability is better than that between the pore radius, porosity and permeability. Moreover, the pore throat radius of the dominating diagenetic facies is more uniform, with better connectivity and seepage ability, which keep high mercury saturation under the same pressure of the mercury intake. The logging response characteristics of the different diagenetic facies are summed up by using natural gamma ray, sonic time difference, resistivity and other logging curves. We then established the logging response identification template for each diagenetic facies, and determined the quantitative identification criteria for logging response of the different diagenetic facies. With that, we identified and divided the vertical upper diagenetic facies of the single well, which provide an important reference for the prediction of sweet spot in low permeability sandstone reservoirs.

Features of Microscopic Pore Structure and Their Influence on Oil Displacement Efficiency in Chang 8₁ Reservoir of Xifeng Oilfield, Ordos Basin

LI Pan, SUN Wei, WANG Zhen, HUANG Hexin, ZHE Wenxu

2018, 32(06):  1194-1202.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.08

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High heterogeneity in pore structure, rapid rise in water content and high pressure in water injection are reported at the Chang 8₁ reservoir in the Xifeng Oilfield, Ordos Basin. We present detailed experimental study on the features of the microscopic pore structure and its influence on the oil displacement efficiency. The techniques employed include grading analysis, physical property measurement, X-ray diffraction (XRD), thin section casting, SEM, high pressure mercury penetration and water-driven displacement test with real microscopic sandstone models. Based on the capillary pressure curve and its corresponding parameters, we divide the pore structures of Chang8₁ reservoir into four types, i.e.A, B, C and D. Our research shows that different pore structures correspond to different reservoir storage space. There are significant differences among the four types of the water flooding paths and oil displacement efficiency. Pore throat radius is the key that affects oil displacement efficiency. Oil displacement efficiency increases with permeability and porosity. Meanwhile, better reservoir rock pore structure correlates with higher oil displacement efficiency. Comprehensive analysis shows that the relationships between the feature of the microscopic pore structure and the oil displacement efficiency provide a reliable basis to find prospective reservoirs and enhance our understanding on them.

Experimental Study on the Solvent-Assisted Steam Gravity Drainage Process in Extra-heavy Oil Reservoirs

WANG Liangang, SHI Lanxiang, YUAN Zhe, LI Xiuluan, LIU Pengcheng

2018, 32(06):  1203-1211.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.09

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Based on an extra-heavy oil reservoir in China, experiments of Steam Assisted Gravity Drainage (SAGD) were carried out with a two-dimensional apparatus. We present new findings on the effects of solvents on the characteristics of steam chamber development, production rate and oil recovery. Our results show that liquid and gaseous components in the solvent co-exist in the oil reservoir. The mass quantity of the gaseous components was higher when higher concentration of solvent was injected. The gaseous components in the reservoir are accumulated in the top of the reservoir, reducing the heat loss and improving the conformity of the steam chamber shape in the vertical plane. Solvent-assisted SAGD has greatly improved the peak oil rate with proper concentration. Energy consumption per unit oil production in the low concentration solvent assisted SAGD process is significantly lower than that in the pure SAGD process. This study shows that solvent-assisted SAGD has great potential in recovering extra-heavy oil reservoirs.

Petrology

Age and Geochemistry of the Early Cretaceous Intrusive Rocks in Southern Tahe, Northern Great Xing’an Range

XU Liming, WANG Dake, LIU Yu, ZHENG Jilin, ZHANG Wenqiang, LIANG Zhongkai

2018, 32(06):  1212-1226.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.10

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This paper presents zircon U-Pb dating, in-situ zircon Hf isotopic and geochemical data for the intrusive rocks from southern Tahe, northern Great Xing’an Range, to constrain their petrogenesis and tectonic settings. The rocks consist of a continuous mafic to felsic magmatic suite (SiO₂=51.27%-74.90%). Zircon U-Pb dating indicates that the two intrusive rock samples analyzed were emplaced in the Early Cretaceous (126.9±0.8) Ma and (123.4±0.9) Ma). In the Harker diagrams, most of the major elements and trace elements have a good linear evolutionary trend with increasing SiO₂ content (except K₂O and Rb). The rocks are generally enriched in Pb and LILEs (K, Rb, Ba), depleted in HFSEs (Nb, Ta, Ti, P), and have similar Sr and Nb isotope characteristics (⁸⁷Sr/⁸⁶Sr_i=0.705,517-0.706,827, ε_Nd(t)=-6.82-0.79). This indicates that the Early Cretaceous intrusive rocks in southern Tahe derived from a mixed source of garnet lherzolite (predominant) and spinel lherzolite, which were metasomatized by subduction-related fluids or melts. During the rapid magma ascent, the magma has experienced fractionation, eventually forming a broad compositional spectrum of rocks. The paper reviews the distribution of volcanic rocks in northeast China, paleomagnetic data, the timing of the Mongolia-Okhotsk ocean closure and the subduction direction of the Paleo-Pacific Plate. These data imply that the Early Cretaceous intrusive rocks in southern Tahe were likely formed in a post-collisional setting after the closure of the Mongolia-Okhotsk ocean.

Mineral Chemistry of Husite Pluton in West Tianshan, Xinjiang and Its Implications for Petrogenesis and Mineralization

HE Yu, ZHANG Yongmei, GU Xuexiang, PENG Yiwei, CHENG Wenbin, WANG Guannan, WAN Yu, YUAN Peng

2018, 32(06):  1227-1241.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.11

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The Husite pluton is situated on the middle-northern margin of the Boluokenu island arc in the West Tianshan, Xinjiang, and is a typical skarn mineralization-related intermediate-felsic intrusive complex in the eastern Boluokenu ore belt. In this paper, we systematically studied the mineral chemistry of monzogranite, granodiorite and mafic enclaves from the Husite pluton, and discussed the magmatic evolution and the relationship between mineral composition and petrogenesis and metallogenesis. Rock-forming mineral compositions show that the Husite granites are typically I-type formed in a continental arc setting, and was mainly derived from partial melting of the lower crust with mantle-derived input. The Husite pluton was formed under relatively high temperature (738-770 ℃), low pressure (0.57-1.42 kbar) and oxidizing environment. The shallow emplacement (2.2-4.2 km deep) of oxidized monzogranitic and granodioritic magmas likely facilitated the Kekesala-Aimusidaiyi Fe-Cu ore formation. The Mg-enrichment and high oxidation coefficient of biotite, and the Mg-Si-enrichment and wide compositional range of amphibole in these rocks are both compositional features related to Fe-Cu mineralization. Magma mixing may have been closely related to the ore formation, and is also indicative for porphyry-skarn polymetallic prospecting in the region.

Review of Geochemical Characteristics of Jingshan-Tushan Granites in Bengbu Uplift, Southeast Margin of North China Craton

KANG Congxuan, YANG Xianzhong, CAI Yitao, ZONG Wen, HUANG Xianjue, KONG Guanglin, LI Chaowei

2018, 32(06):  1242-1253.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.12

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In this study, we carried out field observation, geochronological and geochemical analyses on the Jingshan-Tushan granites in the Bengbu uplift, southern margin of the North China craton. Zircon U-Pb dating of the weakly-gneissic monzogranite yielded (160.4±1.3) Ma to (162.8±1.8) Ma, suggesting Late Jurassic magmatism. Lithogeochemical data show that the Jingshan-Tushan granites are overall Si- and alkali-rich, high-K calc-alkaline, metaluminous-peraluminous, relatively LREE-enriched, with strong positive Eu anomalies and subtle Ce anomalies. The granites are also depleted in K, P and Ti, and relatively enriched in Rb, Ba, U, La, Sr, Zr and Sm. Data points of the granites fall into the I-type field in the petrogenetic discrimination diagram, and zircon Lu-Hf and whole-rock Sm-Nd compositions suggest that the magma source may have been mainly derived from the Neoarchean continental crust. In tectonic discrimination diagrams, the data points fall mainly in the volcanic arc granite field. It is suggested that the granites were formed in a post-collision extensional setting, consistent with the geodynamic background of the Late Jurassic North China craton.

Geochemical Characteristics and Tectonic Setting of Meta-mafic Volcanic Rocks from Jixian Group in Liujiaping,Wenxian County, Gansu Province

MAO Yanli, WANG Tao, LI Hongrui, PAN Zhongkui

2018, 32(06):  1254-1262.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.13

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Detailed field geological survey suggested that the Jixian Group volcanic rocks in Liujiaping are mainly meta-basalts. Geochemical analysis showed that the rocks are aluminum unsaturated (average A/CNK=0.59%) and sodic (Na₂O/K₂O=47.00-144.00). In the TAS diagram, the basalts are sub-alkaline. In the AFM diagram, the samples fall into the tholeiitic basalt field. The total REE contents (∑REE) vary in the range of 58.22×10^-6-95.59×10^-6(average 67.81×10^-6 ). The rocks show anomalies of Eu (δEu=0.83-1.17) and Ce (δCe=0.88-0.95), with flat chondrite-normalized REE distribution pattern. The trace element geochemistry is characterized by distinct depletions of Zr, P, Y and Yb, and relative enrichments of Th, Hf and Nb. There is also strong depletion in K and relative enrichments in Rb and Ba. The values of Zr/Y are 2.38-3.91; Ti/Zr are 92.30-147.23; and Th/Ta are 1.77-2.21, more than 1.60. The meta-basalt yielded a whole-rock Sm-Nd isochron age of (1,387±32) Ma. Based on geochemical tectonic discrimination and regional geological background, it is considered that the Jixian Group meta-basalts in Liujiaping were formed in an island arc setting, which is important to the tectonic evolution study of the Bikou terrane.

Zircon U-Pb Age and Lithogeochemical Characteristics of Late Triassic Dacite in Sanchahe Area, Fengqing County, Western Yunnan Province

LI Guochang, WANG Wei, YANG Ligang, TIAN Yinggui, FEI Zhibin, LI Weizhong

2018, 32(06):  1263-1271.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.14

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Volcanic rocks in Sanchahe area are mainly composed of dacite. LA-ICP-MS zircon U-Pb dating indicates that the dacite was formed in 209.7-218.8 Ma. Many inherited zircon cores of different periods were found, suggesting that the dacite have had complex magma source. The dacite contains high Si and Al contents, and belongs to high-K calc-alkaline series. The rocks show strongly fractionated REE pattern, medium negative Eu anomalies, depletions of Ta, Ba, Nb and Sr and enrichments of Rb and Th. This suggests that the dacitic magma was originated from the anatexis of crustal source. Integrating geochemical and geochronological results, we propose that the Sanchahe dacite formed in a post-collision extensional setting after the Paleo-Tethys closure.

Ore Deposits

The Existence and Effect of Organic Matter in the Mineralization Process of Mayuan Pb-Zn Deposit, North of the Yangtze Plate, China

SONG Zhijiao, CHEN Cuihua, YIN Li, ZHANG Yan

2018, 32(06):  1272-1282.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.15

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Mayuan lead-zinc deposit is located in the east of Micangshan tectonic belt, the northern margin of the Yangtze plate, which is one of the most important lead-zinc deposits in this area. The ore body is hosted in the Sinian Dengying Formation breccia dolomite, and there is a large amount of bitumen associated with sphale-rite and galena in ores. In order to explore the effect of organic matter on lead-zinc mineralization in Mayuan lead-zinc deposit, detailed study of mineralogy, petrography, microthermometry and systematic analysis of laser Raman spectra and carbon isotopic compositions were carried out on bitumen, ores and surrounding rocks. The results show that there are a large number of organic inclusions in the deposit, and the organic inclusions are composed of CH₄, C₂H₆, H₂S, CO₂ and other components. The result of homogenization temperature of inclusions, the maximum palaeotemperature calculated by vitrinite reflectance of bitumen and carbon isotopic compositions show that the organic matter in the deposit may be formed by thermal cracking of the paleo-oil reservoir once existed in the Sinian Dengying Formation. The thermal cracking of the paleo-oil reservoir provided a reduction environment and a reduction sulfur for lead-zinc mineralization.

The Ore-forming Material of the Erdaogou Gold Deposit in West Liaoning Province: Evidence from S-Pb Isotopes

NIE Fei, LIU Shusheng, DONG Guochen, CHEN Yongchang, WANG Peng

2018, 32(06):  1283-1291.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.16

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The Erdaogou gold deposit in West Liaoning Province is located in the middle segment of north margin of North China Craton. The mineralization type is quartz vein type, and the occurrence of ore vein is controlled by fault. In this paper we study S and Pb isotopes in detail on the typical quartz vein to discuss the ore-forming material source. The δ³⁴S values of the total S isotope for the ore-forming hydrothermal fluids are quite similar to those of the mantle, suggesting that the sulfur of the ore-forming hydrothermal solution was derived from hypomagma. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb values of ores range from 17.047 to 17.292, 15.319 to 15.555 and 36.991 to 37.855, respectively, suggesting that the ore lead was from mantle and lower crust. The S and Pb isotope values are similar to those of the rocks of Xiduimiangou, so we deduce that the sources of ore-forming material are strongly associated with the Xiduimiangou rock (or this magmatism). All the evidences support that metallogenic materials were derived from hypomagma.

Geochemistry

Geochemical Characteristics and Influencing Factors of Selenium in Soils of South Jiangxi Province:A Typical Area of Qingtang-Meijiao

ZHOU Mo, CHEN Guoguang, ZHANG Ming, ZHAN Long, LIANG Xiaohong, ZHANG Jie, SUN Zhongcong, YONG Taijian, TANG Zhimin

2018, 32(06):  1292-1301.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.17

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A detailed investigation of selenium concentration and distribution in the soil was carried out in Qingtang-Meijiao area, South Jiangxi Province. 889 topsoil (0-20 cm) samples and 72 crop samples were collected. We systematically analyzed the distribution of selenium in the soils and crops, the relation between the distribution characteristics and soil parent materials, land-use type, physical and chemical properties of soils. Results of the analysis show that the average contents of soil selenium in the study area was 0.44 mg·kg^-1, including 48.59% in sufficient selenium state, and 42.86% in rich selenium state. In spatial distribution, the area which showed deficiency or potentially insufficient of selenium is only sporadically distributed. The contents of selenium in topsoil inherited the soil parent material partly. Furthermore, the concentrations varied in diffe-rent land use types. Correlation analysis showed that selenium contents in soils had a significant positive correlation with organic material and a faint correlation with pH value. Peanut and rice have higher selenium enrichment rates. The rich selenium rates of the peanut and the early season rice both meet the national food safety standards. Only late season rice expressed excessive heavy metals. By comparing data, we found that the over-standard rate of heavy metals in late season rice collecting from selenium-rich areas was far lower than those from non-selenium-rich areas. It is indicated that the selenium in soils can partly reduce the enrichment effect of heavy metal elements in late season rice.

Study on Concentration Characteristics and Influencing Factors of Heavy Metals in Soils in Longhai, Fujian Province

SUN Kai, SUN Binbin, ZHOU Guohua, HE Ling, ZENG Daoming, WU Chao, CHENG Xiaomeng

2018, 32(06):  1302-1310.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.18

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To prevent ecological risk from heavy metals in soils in Longhai County, heavy metal concentration and their speciation characteristics as well as influencing factors of heavy metals were studied by classic statistical methods and random forest. The results show:(1) most heavy metals are enriched in paddy soils derived from Quaternary alluvial, deluvial or marine sediments;(2) the available contents of heavy metals in red soils in hilly and mountainous areas are relatively higher, which are derived from acid rock in Yanshanian age;(3) the speciation contents of As,Cu and Ni are correlated with their total contents, but the correlation is poor for Cd, Cr and Hg;(4) except for the total amount of elements, the effects of soil physico-chemical properties on the speciation of heavy metals are varied significantly. It presents that soil organic matter have great impact on the fraction contents of heavy metals of weak-bound to organic matter(except for Ni, Pb) as well as ion exchangable and carbonate-bound fractions of Cd and Zn. The cation exchange capacity has effect on all forms of Ni. The ratios of (Fe×Al)/Si have effect on the fractions of Cu. However, soil origin and soil type seems to have little effect on heavy metal fractions. The study shows that the labile fraction of heavy metals is not corresponding to their total contents in most cases. Therefore, it is necessary to consider the speciation characteristics of heavy metals in soil when assessing their ecological risk.

Spatial Variation Analysis of Soil Nutrients in Lixian Town of Daxing District in Beijing Based on Geostatistics and GIS

AN Yonglong, DU Zitu, HUANG Yong

2018, 32(06):  1311-1321.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.19

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Spatial variation and distribution of parameters related to soil nutrients in Lixian, Daxing district in Beijing were investigated by geostatistics and GIS. These parameters include total nitrogen, total phosphorus, total potassium, total boron, alkaline hydrolyzable nitrogen, available phosphorus, available potassium, available boron, organic matter and pH. The results reveal strong variations in available phosphorus, available potassium, and alkaline hydrolyzable nitrogen with variation coefficients of 105.99%, 100.43%, and 80.29%, respectively. The integrative comparison of interpolation error in order-index under different trends has been made. It indicates that the spatial variations of total phosphorus, available phosphorus,total potassium, available potassium, total boron, and available boron are characterized by first-order trend. While that of total nitrogen shows second-order trend and no trend is observed in alkaline hydrolyzable nitrogen, organic matter and pH. The spatial variations of total phosphorus, available phosphorus, total potassium, total boron and pH fit exponential model. While those of available potassium, total nitrogen, alkaline hydrolyzable nitrogen, available boron and organic matter fit linear model. The total phosphorus, available phosphorus, total potassium, total boron and pH are mainly influenced by structural factors. The total nitrogen, available boron and organic matter are controlled by both structural and stochastic factors. While available potassium, alkaline hydrolyzable nitrogen are only influenced by stochastic factors. In the ordinary Kriging interpolation diagram, distribution patterns of element contents in the soil reveal the same spatial distribution for total nitrogen, alkaline hydrolyzable nitrogen, total phosphorus, available boron, organic matter and available phosphorus, as well as for total potassium and available potassium. The total boron has distinct distribution that is different from other elements. This is in agreement with the result of the statistical analysis. Understanding the spatial distribution of the ten nutrient indicators in soil is essential to adjusting the ratio of fertilizer consumption and achieving targeted fertilization. It also provides data support for the structural adjustment and standardized layout of agriculture industry.

Study on Mobility of Chitosan Coated Fe/Ni Bimetal Nanoparticles and Their Reactivity for Trichloroethylene Degradation in Groundwater

ZHOU Xuanyi, LI Zhe, CHEN Jiawei

2018, 32(06):  1322-1328.  DOI: 10.19657/j.geoscience.1000-8527.2018.06.20

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Trichloroethylene (TCE) poses a serious threat to the public health and environmental safety. In-situ injection of nano zero-valent iron (nZVI) can be used to degrade TCE in groundwater. However, in application, nZVI is easy to be oxidized and aggregated, resulting in loss of reactivity and poor mobility. Accordingly, in the present study, we used the natural polymer chitosan as a coating agent to increase the dispersion and stability, and loaded nickel as a catalyst to enhance the reactivity. A chitosan-coated nano-iron-nickel bimetallic particle (CS-Fe-Ni) was successfully prepared. The spectrum of CS-Fe-Ni sedimentation showed the dispersion and stability of nanoparticles were improved. The Zeta potential analysis indicated that the negative charge of particle surface increased due to coating chitosan, which promoted the electrostatic repulsion among the nano-particles and the dispersion stability of CS-Fe-Ni. The column experiments showed the mobility of modified CS-Fe-Ni was largely improved. The batch experiments showed that CS-Fe-Ni can be able to highly degrade TCE for complete dechlorination. The results obtained from this study provided the theoretical and experimental basis for the application of nZVI in-situ remediation technology.