Table of Content

10 August 2018, Volume 32 Issue 04

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Ore Deposits and Geochemistry

Fluid Inclusions and Isotopic Geochemistry Characteristics of the Xiaotongjiapuzi Gold Deposit, Liaoning Province, China

LIU Jun, LIU Fuxing, LI Shenghui, DUAN Chao

2018, 32(04):  631-645.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.01

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The Xiaotongjiapuzi gold deposit is located in the northern North China Craton, eastern Liaoning Province, NE China. The strata in the Xiaotongjiapuzi gold deposit are composed of the marble and schist of the Dashiqiao and Gaixian formations of the Proterozoic Liaohe Group. The faults control the distribution of the ore bodies. The ores contain quartz vein and altered rock types. The wall-rock alterations in the deposit can be divided into silicification, sericitization and carbonatization. Three stages of mineralization were identified, with the early stage represented by quartz±pyrite vein, the middle stage by quartz-polymetallic sulfide vein, and the late stage by quartz-carbonate vein. Four types of fluid inclusions were distinguished: liquid-rich two-phase, gas-rich two-phase, CO₂-bearing and pure CO₂ fluid inclusions. The early stage quartz only contains liquid-rich two-phase fluid inclusions with salinities of 5.9 to 14.3 wt.% NaCl equiv. and homogenization temperature of 311 to 408 ℃. The middle stage quartz contains all four types of fluid inclusions, of which liquid-rich two-phase, gas-rich two-phase, CO₂-bearing fluid inclusions yield homogenization temperatures of 268 to 376 ℃, salinities of 4.1 to 13.0 wt.% NaCl equiv. In the late stage quartz only the liquid-rich two-phase fluid inclusions were observed, which have relatively low salinities of 1.6 to 7.6 wt.% NaCl equiv. and relatively low homogenization temperatures of 201 to 254 ℃. The ore-forming fluid is characterized by medium temperature, low salinity and CO₂-rich, roughly belonging to H₂O-NaCl±CO₂ system. The fluid phase separation or immiscibility in the middle stage caused rapid precipitation of ore-forming materials. The δ¹⁸O_W values of the ore-forming fluid vary from 0.3‰ to 2.3‰, and δD_W values vary from -99.8‰ to -96.2‰, indicating that the ore-forming fluid derived mainly from magmatic fluid mixed with minor metamorphic water and meteoric water. δ³⁴S of metallic sulfides ranges from +4.6‰ to +12.9‰. Pb isotopic ratios of metallic sulfides show small variations: ²⁰⁶Pb/²⁰⁴Pb=17.671 to 18.361, ²⁰⁷Pb/²⁰⁴Pb=15.569 to 15.659 and ²⁰⁸Pb/²⁰⁴Pb=37.695 to 37.937. Sulfur and lead isotopes suggest that the ore-forming materials were derived from the metamorphic rocks of the Liaohe Group and Late Triassic magmatic rocks. ³He/⁴He ratio of fluid inclusions in pyrite ranges from 0.27 to 0.53 Ra. The mantle helium involved in the ore-forming fluid is 2.9% to 5.8%, which implies mantle-and crust-derived fluids were involved in the gold mineralization together.

The Metallic Minerals and S and Pb Isotope Compositions of the Harizha Lead-Zinc Polymetallic Deposit, East Kunlun

ZHANG Bin, YANG Tao, YANG Shengfei, LI Jinchao, KONG Huilei

2018, 32(04):  646-654.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.02

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The Harizha lead-zinc polymetallic deposit is located in the eastern part of the East Kunlun orogenic belt, closing to the north side of the central Kunlun fault. The reported data show that the Harizha lead-zinc polymetallic deposit has a good prospecting potential. This paper focuses on the temperature and source of ore-forming materials, based on the studies on the characteristics of metallic minerals and their S-Pb isotopes from the Harizha lead-zinc polymetallic deposit. The data show that the content of Fe in sphalerite ranges from 9.751% to 12.736%,and the range of Zn/Cd value is 56.50 to 114.39, suggest that the Harizha lead-zinc polymetallic deposit is a medium-low temperature deposit; The δ³⁴S values of sulfide minerals in the deposit range from -3.8‰ to -0.5‰, indicating that sulfur is sourced from the deep-source magma,and the S in different sulfides are not in equilibrium. The ²⁰⁶Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of sulfide ores are 18.254-18.504, 15.614-15.800 and 38.429-39.028, respectively, which suggest that the ore-forming materials were mainly derived from the parental magma generated by mixing of mafic magma and felsic magma formed by remelting of lower crustal rocks.

Soil Geochemical Characteristics and Prospecting Direction in Elegenwulanwula Area of Beishan District,Inner Mongolia

ZHANG Shanming, LAN Shengke, HE Zhongyin, HAN Zhiming, CHEN Qiang, WANG Yonghui

2018, 32(04):  655-666.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.03

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The study area is located in the north zone of Beishan Mt,where the ore-forming geological condition is favorable, and the anomalies of the 1∶200 000 stream sediment survey are outstanding. Meanwhile, the Elegenwulanwula porphyry Mo(Cu)deposit is also located in this area, where the 1∶50 000 soil geochemical survey has been conducted by the authors. Taking the soil geochemical data as the material and the geology cognition as the basis, this paper has studied the geochemical data characteristics, geochemical field characteri-stics and integrated anomalies characteristics. According to this study,the authors believe that Mo, Cu and Au are the main metallogenic elements in this area, the volcanic horizon of Xianshuihu Formation is the main meta-llogenic strata, and the Carboniferous granodiorite is the main metallogenic intrusion. All the integrated anomalies can be divided into five types, among which those related to the porphyry Mo(Cu)metallogenic system and Ordovician geological formation-structure are the key points for the future study and prospecting.

Petrology

Geochemical Characteristics and Tectonic Significance of Shibandun Mafic-ultramafic Cumulates in Western Part of the Central Qilian

MA Zhen, LIU Zheng, LIU Yixin, WANG Jinrong

2018, 32(04):  667-679.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.04

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The Shibandun mafic-ultramafic cumulates are widely distributed in the western part of the Central Qilian, north of the Danghenanshan fault zone. The mafic-ultramafic cumulates comprise multiple sequences of (from bottom to top) peridotite, olivine pyroxenite, gabbro, magnetite and diorite. LA-ICP-MS zircon U-Pb dating of the gabbro yielded a mean ²⁰⁶Pb/²³⁸U age of (486.5±3.3) Ma. Geochemical analysis indicates that serpentinized olivine pyroxenite has similar multi-element patterns to the gabbros, and they both show large ion lithophile element (LILE) enrichments and high field strength element (HFSE) depletions. They are also relatively enriched in LREE, and with flat HREE patterns and positive Eu anomalies (0.97-3.64). The study shows that the Shibandun mafic-ultramafic cumulates were likely co-magmatic, and the magma was likely derived from the subduction fluid-metasomatized asthenospheric mantle.The magmatic evolution process may have involved repeated cycles of magma fractionation, cumulate formation and basaltic magma replenishment.The Shibandunmafic-ultramafic cumulates were likely formed in volcanic arc setting.Integrated with the regional tectonic background, we propose that the western part of the Central Qilian microcontinent was likely a volcanic arc accretionary complex that was formed on the residual microcontinental margin.

LA-MC-ICP-MS U-Pb Geochronology and Petrogenesis of Plutons in Baliersi River Area of Altay and Their Geological Implications

ZHU Bopeng, QIN Jihua, HE Bin, ZHANG Hanqing, WU Xiaogui

2018, 32(04):  680-691.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.05

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Rock types in the Baliersi River area of the Chinese Altay Orogen (Xinjiang) are complex, including granodiorite, biotite monzogranite and monzogranite. LA-MC-ICP-MS zircon U-Pb dating reveals that the granodiorite and monzogranite were formed at (386.4±2.8) Ma and (386.8±1.2) Ma, respectively. Geochemical analysis of the granodiorite, biotite monzogranite and monzogranite show that the SiO₂ contents range from 74.33% to 76.70%, Rittman index (σ) range from 1.49 to 2.04, and the A/CNK values range from 1.00 to 1.07. In addition, the rocks show enrichments in LILEs (e.g., Rb,Th) and LREEs, and obvious depletions in HREEs and HFSEs (e.g., Sr, Ti, Nb) and strong negative Eu anomaly (δEu=0.31 to 0.84), suggesting that the rocks are high-K calc-alkaline, peraluminous highly-fractioned I-type granites. Integrated with previous studies, it is concluded that granitoids in the Baliersi River area were formed in a continental margin magmatic arc setting, via the north-dipping subduction of the Paleo-Asian Ocean.

Discovery of Bimodal Volcanics and Its Geological Significance in the Xiemisitai Region, Western Junggar, China

WENG Kai, MA Zhongping, ZHANG Xue

2018, 32(04):  692-703.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.06

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The Xiemisitai region in the Western Junggar is a key region to investigate the tectonic evolution of the Junggar ocean basin. The discovery of the Xiemisitai bimodal volcanics and their composition, petrogeochemistry, and zircon U-Pb age are important to discriminate formation mechanism and tectonic setting, reconstruct the tectonic framework of Western Junggar orogenic belt. The following acquaintances were obtained by this paper.The bimodal volcanics are composed of alkaline basalt and calc-alkaline rhyolite, and the LA-ICP-MS zircon U-Pb dating of the rhyolite is (431.8±2.3) Ma. The mafic magma was likely derived from partial melting of the mantle metasomatized by subduction-related fluid, and the felsic magma was derived from the partial melting of crust materials. The bimodal volcanics may have formed in an early Silurian incipient back-arc basin. Combined with previous studies, we suggest that there was a complete Early Paleozoic trench-arc-basin system in the Xiemisitai region, Western Junggar.

Petrogenesis and Tectonic Implications of Late Triassic Volcanic Rocks at the Gansu-Qinghai Junction in the West Qinling Mountains

LIU Bochong, LI Kangning, SHI Hailong, PU Wanfeng, WANG Hongtao, WANG Shuheng

2018, 32(04):  704-717.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.07

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Volcanic rocks are developed in the West Qingling Mountains, near the border between Gansu and Qinghai Provinces. The rocks are dominantly andesitic and rhyolitic, and are all high-K calc-alkaline volcanic rocks.These volcanic rocks differ greatly in their major and trace element contents. The SiO₂ contents range from 56.67% to 78.17% (average 69.78%). The Al₂O₃ are high (12.77% to 17.29%,average 14.64%) and the TiO₂ contents are low (0.02% to 0.75%, average 0.22). The Na₂O/K₂O ratios are low (0.03% to 2.68%,average 0.65%). Light rare earth elements (LREEs) are enriched whereas heavy rare earth elements (LREEs) are depleted. REE patterns are obviously right inclining with distinct negative Eu anomalies. The chondrite-normalized HREE patterns of the andesitic and rhyolitic volcanic rocks are markedly different, which implies that the both volcanic rock types were derived from different magma sources. The volcanic rocks are depleted in high field strength elements(HFSEs) such as P,Nb,Ti, and Ta, but are enriched in large ion lithophile elements (LILEs) such as Th,Ba,K, and Rb. LA-ICP-MS zircon U-Pb dating of the andesitic volcanic rock yielded (236±1.2) Ma,which represents the volcanis mage.These rocks were likely oceanic subduction products with high-degree partial melting in the deep mantle, and the magma is also influenced by fractionation and crustal assimilation during its ascent. The volcanism may have formed in an active continental margin arc setting, related to the south-dipping subduction of the Longwu Gorge Ocean(remnants of which preserved now as ophiolite). Magmatic evolution of these volcanic rocks was likely controlled by partial melting and fractional crystallization: the andesitic magma was mainly controlled by fractional crystallization, whereas the rhyolitic magma was largely dominated by partial melting.

Classification and Geological Significance of the Upper Jurassic Haritaolegai Formation Basalt in the Northern Da Hinggan Mountains

ZHAO Shengjin, GAO Lidong, YU Haiyang, PIAO Lili, LIU Zhihui, ZHOU Yingshuai, ZHANG Meng, ZHANG Yulong, YANG Haixing, ZHAO Wanli

2018, 32(04):  718-726.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.08

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The Upper Jurassic basaltic rocks of the Haritaolegai Formation were firstly identified in the western part of the northern Da Hinggan Mountains, with the rock assemblage including black/dark gray/purplish brown basalt, amygdaloid basalt, alkaline olivine basalt and basaltic trachy and esite. SHRIMP zircon U-Pb dating of the basalt yielded Late Jurassic age of (146.7±3.1) Ma.Lithogeochemical data show that the rocks are high-K calc-alkaline. The basalts contain low content of Sr,and show enrichments in high large ion lithophile elements (LILEs,such as Rb, K and Ba) and depletions in high field strength elements (HFSEs, such as Nb and Ti).The rare-earth element (REE) contents are generally high,yet the REE fractionation is unclear and the rocks contain slightly negative Eu anomalies. Based on the regional geological survey and strata contrast, the Upper Jurassic Haritaolegai Formation basalt is confirmed to fit the definition of the ever used Yiliekede Formation, so they are the same petrographic composition. Therefore, this study suggests that the Yiliekede Formation should be resumed, and the confirmation of this formation is of great geological significance for the study of tectonic-magmatic activities in the Mesozoic and the comparison of Mesozoic volcanic strata in the study area.

Zircon U-Pb Geochronology and Geochemistry of Granitic Mylonites in Fengqing, Yunnan Province

WANG Hong, CONG Feng, LI Zaihui, WANG Hailin

2018, 32(04):  727-738.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.09

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Based on field investigations, new data on the geochronology, petrology and geochemistry of the Fengqing granitic mylonites (north of Lincang batholith) located in southern Sanjiang region are presented. LA-ICP-M zircon U-Pb dating of two Fengqing granitic mylonites are yielded Triassic ages of (223.3 ±0.50) Ma, and (231.9 ±1.8) Ma, much younger than the previously conceived Proterozoic age. Geochemical analyses show that the granitic mylonites are peraluminous (A/CNK=1.54-1.75),high-K calc-alkaline, with low Na₂O/K₂O ratio. The rocks are enriched in light rare earth elements (LREE), and depleted in heavy rare earth elements(HREE), with distinct negative Eu anomalies( Eu/Eu^*=0.27-0.58). The rocks contain low Cr and Ni contents, high Rb, Th, U and Sm contents, and low Zr, Hf and Ti contents. The biotite granodioritic mylonite, compared to the younger granopegmatitic mylonite, is more enriched in Ni, Fe, Mg, Ca and REE. This may reflect the products of co-magmatic fractionation. The Fengqing granitic mylonites and Lincang granite are broadly coeval and geochemically similar, and they show a transitional contact of brittle-ductile shearing in the field. This indicated that the granitic mylonite is part of the Lincang granite before shearing in the Lancangjiang fault zone, rather than being the previously-conceived Proterozoic Damenglong high-grade metamorphic rocks.

Structural Geology and Stratigraphy

Control on Lead-zinc Mineralization Through Superimposing Structural Deformation in the Wuzhishan Area in NW Guizhou

YANG Xingyu, REN Houzhou, LIU Yu, SHAN Yongbo, YANG Kunguang, AN Qi, LAN Anping, TAN Hua, WU Caijin, XIAO Kai, MO Lulu

2018, 32(04):  739-749.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.10

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The Wuzhishan lead-zinc ore district is located at the junction of Puding and Zhijin in Guizhou Province. The district is tectonically situated at the center of the Yangtze craton, close to the western margin of the Jiangnan orogen. Based on the field structural research, this study found that clear differences between the Sinian-Early Paleozoic and Late Paleozoic-Mesozoic structural deformation features, which were controlled or influenced by the Early Paleozoic Caledonian tectonic movement. The structural line of Sinian-Early Paleozoic is EW-trending, gently EW folded with south- or north-dipping cleavages, which shows the NS-trending compressive deformation. Two sets of NS-and NW-trending high-pitched faults were developed in the Sinian-Early Paleozoic, which were obviously restricted that did not crosscut the post-Late Paleozoic sequences. Sinian-Early Paleozoic interlayer gliding and faulting activities control the distribution of lead-zinc orebodies. Regional tectonic stress field was likely changed after the Late Paleozoic, from early NS-trending compression to early Yanshanian WNW-trending(ESE-dipping) thrusting, which superposed and deformed the Sinian-Early Paleozoic structures, and formed the regional NE-trending tectonic pattern. The late-stage fold axis dips mainly to ESE and the faults thrust to WNW, obliquely superposed on the early deformation. The Yanshanian faulting may have promoted the migration and enrichment of the lead-zinc ores.

Characteristics and Formation Mechanism of Structural Deformation in the Paleogene Wenchang Formation in the Panyu 4 Sag, Pearl River Estuary Basin

LIANG Jie, ZHANG Xiangtao, XU Xinming, LUO Ze, WU Jing

2018, 32(04):  750-757.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.11

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Tectonic deformation of the Paleogene Wenchang Formation in the Panyu 4 sag of Pearl River Estua-ry Basin is intense. According to seismic interpretation, fault activity, migration characteristics of the sedimentation center and depression structural analysis, this study concluded that there was a major tectonic movement in the first stage of the Wenchang Formation. Before that, due to the NW-SE stretching, the intense NE-trending faulting may have led to the NE-trending distribution of sedimentation centers. The northern sub-region has the bipolar (E and W) faulted characteristics. The central and southern sub-regions are featured by faulting in the east and structural overlapping in the west. In the first stage of the Wenchang Formation (during which EW-trending faulting was intense) a EW-trending and a NE-trending sedimentation center were formed. The southwestern slope is featured by faulting in the north and structural overlapping in the south. In the northern sub-region, denudation of the central and southern sub-regions was likely changed from strong to weak. Difference in tectonic deformation indicated that the first stage of the Wenchang Formation was the transition period from NW-to NW-trending extension. Furthermore, the stress regime of the tectonic transform surface was the result of the convergence between the Pacific, India and Eurasian plates. This tectonic phenomenon can be found not only in the Panyu 4 sag, but also in other Cenozoic basins of east China.

Division and Correlation of the Jiufotang Formation and Their Rare Fossil-bearing Beds in Western Liaoning, China

WU Zijie, GAO Fuliang, PAN Yuqi, WANG Xuan

2018, 32(04):  758-765.  DOI: 10.19657/j.geoscience.1000-8527.2018.12

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The western Liaoning region is a world-class fossil site, in which the Jiufotang Formation is an important fossil-bearing stratum, hosting the famous Jeholbiota fossils. Through comprehensive research on the many sections and fossil assemblage comparison, the Jiufotang Formation can be divided into three units, i.e., the Xiaotaizi, Baomayingzi and Xiyingzi are fossil-bearing sequences. The lithological characteristics of fossil-bearing beds are directly related to volcanic activities, and the fossil-bearing beds are always located in the top of lithologic cycle. We first propose that there were volcanic eruptions during the deposition of the Jiufotang Formation.

Characteristics of Oolites and Their Dolomitization Mechanism of the Cambrian Zhangxia Formation at Xiaweidian Outcrop in Beijing

GUO Qiheng, JIN Zhenkui, ZHU Xiaoer, WANG Jinyi

2018, 32(04):  766-773.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.13

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The Xiaweidian outcrop in Beijing is a typical Cambrian stratigraphic profile in North China. Previous studies focused mainly on the depositional environment of the Zhangxia Formation, whereas the oolitic types and their diagenesis of the formation are poorly understood. In this paper, field geological and microscopic petrographic observations and XRD analysis were conducted to identify the oolitic types and elucidate the mechanism of oolitic dolomitization.It comes to a conclusion as follows: (1) Major oolitic types include radial ooids, concentric-radial ooids and monocrystalline/polycrystalline ooids, and minor concentric ooids, compound ooids and algae ooids. (2) Oolites are dolomitized whereas the interstitials are not, and the degree of dolomitization in the radial layer is higher than that in the concentric layer.Dolomite particles in the radial layer are radially distributed around the core, and the concentric rings occur around the core. (3) Dolomite grains in the oolites are mostly mesocrystalline or fine-grained, euhedral to subhedral, and returning infiltration of dolomitization was likely the main cause of the oolitic dolomitization, which resulted in a higher degree of dolomitization of the luminescent oolite limestone than the stucco oolite limestone.

Sedimentology

Sedimentary System and the Shale-gas Favorable Area of the Carboniferous in the Nanpanjiang Basin

XIN Yunlu, WANG Jinzhu, JIN Chunshuang

2018, 32(04):  774-785.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.14

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Synthetically utilized the data of key profiles and regional geological survey data, combined with published research results,the sedimentary system types, characteristics and distribution of the Carboniferous in the Nanpanjiang Basin have been discussed, and based on the distribution of deep-water facies, the shale gas favorable areas of the Carboniferous in the Nanpanjiang Basin have been predicted. There were 8 sedimentary systems, such as river delta-clastic littoral, coastal marsh, terrigenous shelf, terrigenous slope, restricted platform, open platform, platform margin, slope and deep sea, developed during Carboniferous in the Nanpanjiang Basin. During Carboniferous, the exposed or denuded area located the uplifts of Maguan, Kangdian, Jiangnan and Yunkai, but the terrigenous supply is relatively small, the terrigenous sediments mainly developed in Early Carboniferous, the carbonate and mud sediments dominated in Carboniferous. During Early Carboniferous, the clastic littoral deposits developed surrounding the Yunkai Uplift, the clastic littoral and the coastal marsh develo-ped in the south margin of the Jiangnan Uplift, the main sedimentary systems consisted of the restricted platform, open platform, platform margin, slope and deep sea. During Late Carboniferous, both the uplift and the deep sea depositional areas are reduced, the open platform range significantly expanded, the restricted platform developed nearby the uplifts. The regions of Nandan-Hechi, western Luodian,Liucheng-Luzai-Pingle and Xiang-zhou-Wuxuan-Guiping, the Upper Paleozoic exposed surface, the Carboniferous shallow buried and dominated by deep sea sediments, are the most favorable areas for the exploration of shale-gas of the Carboniferous in the Nanpanjiang Basin.

Geochemical Characteristics and Geological Implications of Sandstones in Muling Formation of Lower Cretaceous, Laoheishan Basin, Heilongjiang Province

XU Yinbo, LI Feng, ZHANG Jiaqiang, SUN Pingchang, BI Caiqin, TONG Lihua, LI Zhao

2018, 32(04):  786-795.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.15

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The Laoheishan Basin is located in Heilongjiang Province, northeast of China, the coal and oil shale are developed in Muling Formation of Lower Cretaceous. Systematic sampling was made and sandstones of Muling Formation in the Laoheishan Basin were analyzed. The results show that the major elements of sandstones in Muling Formation has the characteristics of Fe₂O₃ less than the FeO, but CaO more than MgO. And the rare earth elements of sandstones show an enrichment in light rare earth elements, a flat trending in heavy rare elements and a negative europium anomaly in most samples. However, there is a significant difference in the enrichment and loss of trace elements between samples. Related discriminations indicate that the source rocks of sandstones were carried and accumulated in short distance which mainly came from felsic rocks of the upper crust without experiencing deposition and recycling. Through the judgment combined with the geochemical characteristic, Dincksion diagram of sandstones and the study of regional tectonic setting, sandstones of Muling Formation have several provenances, and source region majorly was formed in the recycled orogeny and basement uplifted provenances under the tectonic background of active continental margin at the end of Indo-China Movement. Source rocks mostly came from felsic volcanic rocks and intrusive rocks during late Triassic to early-middle Jurassic, with a little probably from metamorphic of late Permian.

Oil & Gas Geology

Quantitative Forecast Method of Reservoir-seal Assemblage for Gas in Deep-water Area with Sparse Wells: A Case Study of Lingshui Depression, Qiongdongnan Basin

LIU Jingjing, LIU Zhen, SUN Zhipeng, SUN Xiaoming

2018, 32(04):  796-806.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.16

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Recent exploration shows that hydrocarbon resources in northern South China Sea are dominated by gas. Compared to oil, the requirement of cap rocks for gas reservoirs is stricter. Therefore, research on the reservoir-seal assemblage for gas is important for hydrocarbon exploration. Using statistics and geoscientific investigation, sandstone reservoir porosity of 12% is defined as the lower limit for the gas effective reservoir in the Qiongdongnan Basin, and the mudstone displacement pressure of 1 MPa was defined as the lower limit for the gas effective cap rock. Based on logging data, we conducted quantitative window forecasting for the reservoir-seal assemblage for gas in a single well, and the results show that one reservoir-seal assemblage window is developed in the well W22-1(Lingshui Depression). We proposed a new quantitative prediction method for reservoir-seal assemblage in the areas with very few or no wells, based on the velocity inversion section. Taking the Lingshui Depression of the Qiongdongnan Basin as an example, we predicted that there is one reservoir-seal assemblage window developed in the depression, which includes the Lingshui-Yinggehai formations. Results of this study broaden the natural gas exploration layers in the Lingshui Depression, and may also be applicable to other deep-water area and underexplored area.

Stratigraphic and Structural Differences and Their Controls in the Shenhu Submarine Canyon,Northern South China Sea

FU Chao, YU Xinghe, HE Yulin, LIANG Jinqiang, KUANG Zenggui, DONG Yisi, JIN Lina

2018, 32(04):  807-818.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.17

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The northern continental slope of the South China Sea (SCS) is the first gas hydrate producing trial region in the SCS,and its stratigraphy would influence the distribution of gas hydrate-bearing sediments. The complex canyon sedimentation and varying stratigraphic styles have hampered stratigraphic correlations in the SCS deep-sea sedimentology study. This study integrated the core-log-seismic data into the stratigraphic boundary identification. Integrating the canyon development stages, we distinguished six four-order stratigraphic boundaries: Sequence (SQ) Ⅲ and SQ Ⅳ were developed with apparent incised valley, and SQ Ⅴ and SQ Ⅵ were influenced by syn-sedimentary faults. Consequently, we classified the stratigraphic boundaries into two main types: sedimentation-driven and subsidence-driven. Sediment-driven sequences can be divided into three system tracts: LST (low stand system tract), TST (transgression system tract) and HST (high stand system tract).This stratigraphic type with abundant sediment supply swashed the basement and formed apparent incised valley. The slope-line trajectory has shown overlapping structures. Subsidence-driven sequence can be divided into four system tracts: LST, TST, HST and RST (regression system tract), and the RST can be distinguished as the regular seismic package between the MFS (Maximum Flood Surface) and incised valley.This stratigraphic type with syn-sedimentary fault development can be shown in the “S” structure in the slope-line trajectory.

Sedimentary Characteristics of Subaqueous Fan in a Faulted Lacustrine Basin:A Case of Typical Blocks in the Downthrown Block of the Southern Dagang Fault

LIU Sheng, LI Shengli, CHENG Tao, ZHOU Xinmao, CAO Rui, ZHANG Qiao, GONG Qiang

2018, 32(04):  819-831.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.18

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Lithology of downthrown block of the southern Dagang fault consists of conglomerate, sandstone, siltstone and mudstone of the 3^rd member of Shahejie Formation. Sedimentary structures include massive structure, cross bedding, soft sediment deformation and some special features, with the presence of charcoal, plant stem, syndepositional faults and argillaceous sandstone clasts. The grain-size cumulate probability curves can be grouped into one-segment and two-segment type. Besides, four types of well-logging-curve patterns, including box-shaped, bell-shaped,funnel-shaped and straight, were indentified. Reflective characteristics of subaqueous fan can be identified in seismic profile. Depending on grain size, electrical and seismic reflections,we concluded that the southern Dagang structure belt has developed subaqueous fans, which can be subdivided into the inner-fan main channel, middle-fan distributary channel, middle-fan inter-distributary bay, the lobe of channel front,subaqueous levee and crevasse. Since the deposition of the 3^rd member of Shahejie Formation, strong activity of the the southern Dagang fault has led to the development of the distal subaqueous fan in the 5^th fault block. Meanwhile, the proximal subaqueous fan existed in the Qinan 9X1 fault block. These two types of subaqueous fans have different sedimentary characteristics in provenance, lithology, electrical property, seismic reflection and morphology. The proximal subaqueous fan is characterized by its fan-shape, paleo-uplift provenance, coarse-grained sediments, box-shaped log curve, strong amplitude and random seismic reflection, and small size and large quantity, while the distal subaqueous fan is featured by its bifurcation shape, delta provenance, fine-graind sediments, bell-shaped log curve, weak amplitude and chaotic seismic reflection, and large size and small quantity.

Reservoir Distribution in the Sulige Large Tight Sandstone Gas Field and Methods for Enhancing Recovery Efficiency of Horizontal Wells

LÜ Zhikai, TANG Haifa, LIU Qunming, LI Xiaofeng, WANG Zelong

2018, 32(04):  832-841.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.19

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Based on the braided river system analysis and reservoir distribution characteristics of the Sulige large tight sandstone gas field, the concept of reserves concentration is proposed and four sand-body distribution models are established, namely the thick block, vertical overlapping panconnected, dispersed partially-connected, and dispersed types. Reservoir recovery of horizontal wells under different sand-body combination is analyzed, and technical measures to improve the recovery rate of horizontal wells are proposed. The results show that straight wells is imperfect due to the blocking zones present in compound sand body of the braided river sedimentary system.Horizontal well can overcome the blocking zone influence and increase the degree of reserve exploitation within the layer.However, the scattered distribution of layered sand bodies and the horizontal well development will lead to insufficient vertical bearing department of gas reserves, and thereby reducing the degree of interlayer recovery. For the greater reserves concentration, thick block and multi-vertical overlapping panconnected types and horizontal well development can significantly improve the degree of reserve exploitation and recovery, of which over 70% are Ⅰ+Ⅱ wells. For the disperse partially connected reservoirs with lower reserve concentration, development of vertical well pattern and optimization of the horizontal well distributions can improve the recovery by more than 10%.

Measurement and Analysis of Oil-water Contact Angle on Several Common Minerals

WU Chunzheng, XUE Haitao, LU Shuangfang, TIAN Shansi

2018, 32(04):  842-849.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.20

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In this paper, the contact angles of oil droplets on mineral surface were determined using contact-angle measuring instrument. The contact angles of different oil types in different mineralizing water and different component oil and mixed-component oil were measured. We proposed a reasonable measurement method to maximize the measurement result accuracy. After measuring the size of the wetting angle, it is found that the lipophilicity of the minerals in the water vary from strong to weak: mica>pyrite>calcite>dolomite>quartz.The type of mineral, oil composition type, water mineralization degree all impose significant influence on the contact angle, and the wetting of oil and water on different mineral surfaces is different. With increasing octadecane content of the oil droplets, the contact angle of the oil droplets on mica surface decreases and the wettability increases. The surface wettability is slightly different on the surface of other minerals. With increasing water mineralization, the contact angle of oil droplets on mica surface increases and the wettability decreases gradually, and the wettability on other mineral surface is also slightly different.

Geophysics

Application of Electrical Prospecting Technology in Extraction Process of In-situ Leaching in Uranium Deposit

HE Ke, ZHAO Yuancheng, LI Jianhua, WANG Gang, YE Gaofeng

2018, 32(04):  850-862.  DOI: 10.19657/j.geoscience.1000-8527.2018.04.21

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In-situ leaching for uranium is an advanced technology which extracts uranium by injecting leaching solution into the ore-bearing formation and pumping lixiviate out from the ore-bearing formation based on the water permeability of the sandstone orebed.Studying the distribution range of the leaching solution below well field will not only help to learn the coverage range of the orebody covered by leaching solution and mining rate, but also be significance to monitoring the underground water pollution. Electrical prospecting methods were carried out in the Uranium In-Situ Leaching(ISL) Test Base in Erlian Basin of Inner Mongolia in order to perform a monitoring test on the course of ISL for uranium. The monitoring tests consist of controlling source audio magneto telluric method (CSAMT) and time domain induced polarization method (TDIP).The test area was divided by an 18×18 survey grid with the both line-line and dot-dot space of 10 m apart. During the test, CSAMT was performed on 5 longitudinal and 4 transverse prospecting lines which crossed through the well unit and TDIP was conducted on the whole well field. A plane polarizability contour map of TDIP and a 2-dimensional apparent resistivity model were obtained after data processing and inversion. Combining the result with the geological information known in the test area, it is considered that the low resistivity anomaly region in the apparent resistivity profile below the pumping well unit is the reflection of the distribution state of the leaching solution underground during the in-situ leaching process, meanwhile,a massive low-polarizability anomaly region in the plane apparent polarizability contour map below the pumping well unit is caused by film polarization effect occurring within the ionic conduction system which consists of leaching solution and rock formation.