Metallogenic‘factories’and resultant highly anomalous mineral endowment on the craton margins of China

The current margins of the North China and Yangtze Cratons provide arguably the best examples globally of anomalously high mineral endowment within a 100 km buffer zone,hosting 66 diverse world-class to giant ore systems that help explain China’s premier position as a producer of multiple metal and mineral commodities.After the cratonization of these crustal blocks during the Neoarchean-Paleoproterozoic,with incorporation of iron ores on assembled micro-block margins,the margins of the cratons experienced multiple convergence and rifting events leading to metasomatism and fertilization of their underlying sub-continental lithospheric mantle.The rifted margins with trans-lithosphere faults provided pathways for Cu-Au(Mo-W-Sn)-bearing felsic to Ni-Cu-bearing ultrabasic intrusions and REE-rich carbonatite magmas,and for the development of marginal sedimentary basins with both Cu-Pb-Zn-rich source units and reactive carbonate or carbonaceous host rocks.There was diachronous formation of hydrothermal orogenic gold,antimony,and bismuth systems in the narrow orogenic belts between the cratons.Complexity in the Mesozoic Paleo-Pacific subduction systems resulted in asthenosphere upwelling and lithosphere extension and thinning in the North China Craton,leading to anomalous heat flow and formation of orogenic gold deposits,including those of the giant Jiaodong gold province on its north-eastern margin.These gold deposits,many of which formed from fluids liberated by devolatilization of previously metasomatized sub-continental lithospheric mantle,helped propel China to be the premier gold producer globally.The thick sub-continental lithospheric mantle of the cold buoyant cratons helped the preservation of some of the world’s oldest porphyry-skarn and epithermal mineral systems.Although craton margins globally control the formation and preservation of a diverse range of mineral deposits,China represents the premier example in terms of metal endowment due to the anomalous length of its craton margins combined with their abnormally complex tectonic history.

Metallogenic Systems on the Paleocontinental Margin of the North China Craton

The North China Craton (NCC) is one of the largest blocks composing the continent. Different types of continental margins well developed around the NCC, along with lots of metallogenic systems of different metals and different times. Based on the study on the structural evolution of the NCC, the authors made a new division of tectonic units of the NCC. Through an analysis of the data of 1:25000 geochemical survey on stream sediments, regional geochemical features of main ore-forming elements including Au, Ag, Cu, Pb, Zn, W, Ni, Co and Mo of the NCC are discussed in the paper. Then different metallogenic systems and their forming processes and geodynamics are discussed in detail. At last, temporal and spatial distribution regularities are summarized and ten favorable ore-control factors on the paleocontinental margins are put forward, including (1) abundance of ore sources; (2) rendezvous of ore-forming fluids; (3) high thermo-dynamic anomaly; (4) remarkable Earth crust-mantle interaction; (5) cluster of macroscopic structures and their long activities; (6) diversity of ore-forming environments; (7) long geohistory; (8) multiforms of critical transitional ore-forming mechanisms; (9) multi-staged and superimposed ore-formation; and (10) suitable preservation condition.

Final-stage Southward Subduction of the Eastern Paleo-Asian Ocean:Evidence from the Middle Permian Mafic Intrusions in the Northern Margin of the North China Craton

The northern margin of the North China Craton(NCC)contains widespread Permian magmatic rocks,but the origin of these rocks remains controversial.This uncertainty hampers us from better understanding of tectonic framework and evolution of the eastern Paleo-Asian Ocean,particularly with respect to its final-stage subduction and closure time.To address these questions,this study presents petrological,zircon U-Pb geochronological,whole-rock geochemical and in situ zircon Hf isotopic data for these Permian mafic intrusions in the northern margin of the NCC.Precise zircon U-Pb dating results indicate that these mafic intrusions were emplaced in the Middle Permian(ca.260 Ma).Geochemically,the studied mafic intrusions have high MgO and transition metals element contents,with high Mg^(#) values,indicating a mantle origin.These mafic intrusions are characterized by enrichments in large ion lithophile elements(LILEs;e.g.,Rb,Ba,and K)and light rare earth elements(LREEs),and depletions in high field strength elements(HFSEs;e.g.,Nb,Ta,and Ti)and heavy rare earth elements(HREEs),indicating that they were formed in a subduction-related setting.These geochemical features,together with zircon ε_(Hf)(t)values(-1.1 to+11.2),indicate that their parental magmas were derived from partial melting of heterogeneous mantle wedge metasomatized by subduction-related fluids,with the contributions of slab sediments.The studied mafic intrusions also show wide range of major and trace elements contents,and variable Mg^(#) values,Eu and Sr anomalies,suggesting that their parental magmas had undergone variable degrees of fractional crystallization.Together with the E-W trending Permian continental arc along the northern margin of the NCC,we confirm that the generation of the Middle Permian mafic intrusions was related to southward subduction of the Paleo-Asian oceanic lithosphere beneath the NCC and the Paleo-Asian Ocean had not closed prior to the Middle Permian.

Paleoproterozoic Multistage Metamorphic Ages Registered in the Precambrian Basement Rocks at the Southeastern Margin of the North China Craton and Their Geological Implications

The Precambrian basement rocks in the Bengbu and neighboring areas, located at the southeastern margin of the North China Craton, occur as granulite terrains and xenoliths in the Mesozoic dioritic porphyry.

Triassic Granitic Magmatism at the Northern Margin of the North China Craton: Implications of Geochronology and Geochemistry for the Tectonic Evolution of the Central Asian Orogenic Belt

The early Mesozoic marked an important transition from collisional orogeny to post-orogenic extension at the northern margin of the North China Craton(NCC). In this study, we undertook zircon U-Pb dating and whole-rock majorand trace-element geochemical analyses of early Mesozoic granitic rocks in the Chifeng area to establish their geochronological framework, petrogenesis, and implications for the tectonic evolution of the eastern Central Asia Orogenic Belt(CAOB). Zircon U-Pb dating results show that these rocks were emplaced in three stages during the Triassic:(1) syenogranites during 250-248 Ma,(2) granodiorites during 244-243 Ma, and(3) monzogranites and granodiorites during 232-230 Ma. These Triassic granitoids belong to the high-K calc-alkaline series and are evolved I-type granites. They have high SiO2 and low Mg O contents with enrichments in light rare-earth elements, Zr, Hf, Rb, Th, and U, and depletions in Ba, Nb, Ta, Sr, and Eu. These geochemical data indicate that the granitoids were derived from partial melting of a lower-crustal source under relatively low-pressure conditions and subsequently underwent extensive fractional crystallization. Considering both the geochemical data and regional geological information, we propose that the 250-248 Ma syenogranites were emplaced in an extensional environment linked to slab break-off after closure of the Paleo-Asian Ocean(PAO) along the Solonker-Xra Moron-Changchun suture zone. The 244-243 Ma granodiorites were formed in a compressional orogenic setting during collision between the Erguna-Xing’an-Songliao composite block and the NCC. The 232-230 Ma granodiorites and monzogranites were emplaced during the transition from compressional orogeny to post-orogenic extension. Overall, the early Mesozoic tectonic evolution of the Chifeng area can be divided into three main stages:(1) closure of the Paleo-Asian Ocean and extension related to slab break-off during the Early Triassic;(2) continuous collisional compression during the Middle Triassic after closure of the PAO;and(3) post-orogenic extension during the Late Triassic, most probably due to lithospheric delamination after amalgamation of the Erguna-Xing’an-Songliao composite block and the NCC.

A ca. 2.2Ga Acidic Magmatic Event at the Northern Margin of the Yangtze Craton: Evidence from U-Pb Dating and Hf Isotope Analysis of Zircons from the Kongling Complex

Objective The Yangtze craton collisional orogeny at ca. extensional events at ca. 1 experienced Paleoproterozoic 1.95-2.0 Ga and post-orogenic 85 Ga related to amalgamation of the Columbia （Nuna） supercontinent （Zhao and Cawood, 2012）. A ca. 2.15 Ga suprasubduction zone ophiolitic melange was recongized in the Archean- Paleoproterozoic Kongling Complex of the northern Yangtze craton （Han et al., 2017）. However, the tectonic evolution in early Paleoproterozoic from 2.4 Ga to 2.2 Ga remains unclear. We report here the presence of a suite of Paleoproterozoic （2.2 Ga） granites in the Huangling dome, northern Yangtze craton, which may provide important insights into crustal growth processes in the craton prior to the assembly of Columbia.

LA-ICP-MS Zircon U-Pb Age of Longtou Syenite body in South Songxian County, Southern Margin of the North China Craton

Objective Indosinian magmatic rocks mainly locate in west Qinling Orogen, which are, however, extremely rare in east Qingling Orogen （Lu Xinxiang, 2000; Zhang Guowei et al., 2001; Guo Xianqing et al., 2017）. The Zhifang Huangzhuang （ZH） area in south Songxian County is located in the southern margin of the North China Craton （Fig. l a）, which is an important lndosinian alkaline magmatic occurrence including 32 syenite bodies and syenitic dykes in east Qinling Orogen. There are five syenite bodes in the ZH area, i.e., the Lang＇aogou, Mogou, Longtou, Jiaogou and Wusanggou from west to east （Fig. l b）.

Petrogenesis of the Early Cretaceous Laojunshan monzogranite at the southern margin of the North China Craton: Constrains on the transition of the tectonic regime

1 Introduction Voluminous Mesozoic magmatic rocks containing abundant Au-Mo polymetallic mineralization resources are developed in the Xiaoqinling-Xiong’ershan district of the southern margin of the North China Craton(NCC).

Neoproterozoic Magmatism in the Northern Margin of the Tarim Craton: Implications for Rodinia Reconstruction

The geodynamic processes for the Neoproterozoic mafic-ultramafic intrusions and dykes in the Kuluketage region,Tarim Craton has also been debated for some time.Some researchers suggested that the Neoproterozoic

An Unique Glomerophyric Diorite Porphyry from the Southern Margin of North China Craton:Geochronology,Geochemical and Quantitative Textural Analysis Constraints

1 Introduction The Wulong glomerophyric diorite porphyry has an extremely peculiar texture with plagioclase phenocrysts clustered as flower-like glomerocrysts(Figs.1a&b),which is never discovered elsewhere of the world.The

Magnetic Fabric Studies of Xiong'er Volcanic Rocks in Southern Margin of the North China Craton and its Implications

The Paleoproterozoic Xiong’er Group is composed of mafic to felsic volcanic rocks and minor sedimentary rocks,distributed along the southern margin of the North China craton(NCC).It is a key marker for regional

内蒙古大青山-盘羊山晚中生代-早新生代构造事件及其对华北北缘构造演化的启示

内蒙古大青山和盘羊山位于华北克拉通北缘,其复杂的地质构造对华北克拉通北部中—新生代构造演化具有重要的指示作用。大青山以北的盘羊山逆冲体系,形成于晚二叠世至早三叠世古亚洲洋的闭合,晚侏罗世可能受蒙古-鄂霍次克洋闭合的影响而重新活动。大青山地区发育4期中—新生代变形构造,从老至新依次是:SE-NW向伸展形成的呼和浩特变质核杂岩、NW向逆冲的大青山逆冲体系、以不变形花岗岩为核心的构造穹窿、大青山山前断裂及高角度正断层。发生于约142~132 Ma的SE-NW向伸展,形成于造山增厚地壳的重力垮塌,并形成呼和浩特变质核杂岩和相关的拆离体系。大青山逆冲体系形成于约130~120 Ma,代表造山过程中地壳荷载与板块汇聚的抗衡导致的构造反转,另一可能是古太平洋俯冲的远程效应。自约120 Ma以来,大青山处于一个构造-热松弛期,导致该区约120~90 Ma的冷却事件被广泛记录,并形成以不变形花岗岩(约114 Ma)为核心的穹窿构造;这些事件可能与华北克拉通的峰期破坏相关。大青山山前断裂和相关的高角度正断层开始于始新世,可能是印度-欧亚大陆碰撞和太平洋板块运动方向改变的远程效应所致。古亚洲洋和蒙古-鄂霍次克洋的闭合导致华北克拉通北缘地壳增厚,引发早白垩世造山晚期的垮塌和伸展,形成呼和浩特变质核杂岩。自120 Ma开始,大青山开始受华北克拉通破坏的影响,并形成后造山伸展。新生代,大青山受新特提斯和太平洋构造域的远程影响。

远震剪切波分裂研究华南西南部上地幔各向异性特征

华南板块由扬子克拉通和华夏地块在新元古代碰撞拼合形成,其西南部的缝合带位置存在强烈争议.本文基于一条南北向宽频带流动台阵天然地震数据,利用SKS波分裂研究华南西南部上地幔各向异性特征的南北向变化.分裂测量结果显示,26°N以南的右江盆地快波偏振方向为E-W或NEE-SWW方向,分裂时差为0.5~2.5 s,变化范围较大;川东褶皱带存在较多空解,快波偏振方向以近东西向为主,分裂时差在0.5~1.5 s范围内变化;在右江盆地北缘和川东褶皱带的过渡区域(约26°N附近)各向异性明显较弱.结合前人的上地幔速度成像结果,我们认为川东褶皱带与右江盆地过渡带是扬子克拉通的南边界,在其下方北侧的川东褶皱带巨厚的岩石圈向南转变成较薄的岩石圈,陡变的岩石圈边界引起了软流圈上涌,软流圈的垂向运动导致其水平方位各向异性较弱.

华北克拉通东北缘改造:来自吉林辉南地区构造热事件的古地磁记录

华北克拉通东北缘处于构造运动活跃地区,古地磁研究可为构造演化和岩浆热事件提供依据。笔者在吉林辉南地区中寒武统32个采点共采集246块样品进行了岩石学、岩石磁学及系统热退磁实验。古地磁实验表明,徐庄组砂质泥岩主要磁性矿物是赤铁矿和磁铁矿,张夏组灰岩主要磁性矿物是颗粒较小的磁铁矿和黄铁矿,且均发生了重磁化,并记录了稳定的中温分量,前者中温分量地理坐标平均方向为D/I=10.9°/50.8°,α_(95)=11.7°,对应的极位置为76°N,264.6°E,A_(95)=13°,与早白垩世岩浆活动记录的古地磁极位置一致;后者中温分量地理坐标平均方向为D/I=29.1°/59.0°,α_(95)=6.5°,对应的极位置为68°N,213.7°E,A_(95)=8.4°,与第四纪火山岩记录的古地磁极位置一致。综合区域地质背景分析,早白垩世—第四纪,吉林辉南及邻区古地磁记录的2次较为强烈的构造热事件,以及因敦化-密山断裂带左旋走滑运动造成的北向运移形成的古纬度差,一定程度上对华北克拉通东北缘起到双重改造作用。

后马场镁铁-超镁铁岩体岩石成因及其对华北克拉通破坏的指示意义

文本通过对华北克拉通东南缘徐宿弧地区后马场镁铁质?超镁铁质岩体进行岩相学、锆石U-Pb年代学、单斜辉石和橄榄石矿物成分、全岩地球化学以及锆石Hf同位素研究,确定该岩体的形成时代、岩石成因及其构造环境,探究华北克拉通深部地幔性质及其演化过程。后马场岩体主要由辉长岩、橄长岩和橄榄辉长岩组成,其中辉长岩LA-ICP-MS锆石U-Pb年龄为109±2 Ma,指示该岩体形成于早白垩世晚期。不同岩性岩石的Si_(2)、CaO、Al_(2)O_(3)、Ti_(2)、Na_(2)O+K_(2)O与MgO呈明显的规律性变化,具有相似的主量元素特征,说明其为同源岩浆演化的产物。后马场岩体相对富集大离子亲石元素(Rb、Ba、Sr),亏损高场强元素(Nb、Ta、Zr、Hf、Ti),具有典型的岛弧型岩浆特征。辉长岩中锆石的ε_(Hf)(t)值为–14.5~5.6,大部分为负值,说明岩浆源区以富集地幔占主导,同时也具有亏损地幔的特征。微量元素Nb/U-Ce/Pb模拟计算结果显示,岩浆发生了80%~90%的上地壳混染,然而岩浆无法同化混染如此高比例的上地壳物质,因此部分地壳物质可能是通过陆壳俯冲并进行源区交代作用进入岩浆。岩石的La/Ba、Th/Yb值与俯冲交代岩石圈地幔相似,Nb/Zr、Th/Zr、Rb/Y和Nb/Y值显示俯冲熔体交代的特征,指示俯冲扬子陆壳衍生熔体交代了岩石圈地幔,在白垩纪古太平洋俯冲板片回卷,岩石圈地幔受到上涌的软流圈地幔的加热,产生的镁铁质岩浆形成了后马场岩体。区域镁铁质岩石锆石ε_(Hf)(t)值的变化规律指示后马场岩体侵位时期是华北克拉通东南缘地幔源区由富集地幔向亏损地幔转折的关键期,在此之后,镁体质岩浆主要源于亏损地幔,因此华北克拉通东南缘早白垩世晚期镁铁质岩浆指示岩石圈地幔源区性质由富集向亏损转变的结束,也代表着华北克拉通破坏的结束。

洛南任家滩—荞麦山正长斑岩成因及其对古元古代晚期裂解的指示——岩石化学及锆石U-Pb年龄和Lu—Hf同位素特征

华北克拉通南缘的陕西洛南—河南豫西地区出露一系列形成于1.8~1.6 Ga的碱性岩,对这些碱性岩的研究有助于提高对华北克拉通南缘古元古代构造环境的认识。笔者等选取陕西省洛南县任家滩—荞麦山一带碱性侵入体进行系统的岩石学、LA-ICP-MS锆石U-Pb年代学、Lu—Hf同位素分析和岩石地球化学研究,讨论了其成因机制和构造背景。研究表明,任家滩—荞麦山岩体的主体岩性为正长斑岩,加权平均年龄为1689±20 Ma(MSWD=0.12),表明其侵位时代为古元古代。该岩体富碱(Na_(2)O+K_(2)O=7.95%~9.5%),高钾(K_(2)O=4.67%~8.51%);稀土元素总量较高(496.15×10^(-6)~650.16×10^(-6),平均543.06×10^(-6)),轻、重稀土元素分馏比较明显,轻稀土元素相对富集(LREE=454×10^(-6)~605×10^(-6)),重稀土元素亏损(HREE=39.3×10^(-6)~45.6×10^(-6)),具有弱负铕异常;K、Rb、Ba、Th富集,Nb、Ta、P、Ti亏损,并且具有明显的Sr负异常。εHf(t)值<0,TDM1值为2038~2218 Ma,TDM2值为2250~2516 Ma,说明岩浆源区物质与富集地幔有关或受到过地壳物质的混染。因此,任家滩—荞麦山岩体是由地幔玄武质岩浆与地壳基底太华杂岩形成的中酸性花岗质岩浆混合后形成的熔体,经强烈的结晶分异作用形成的,其形成于陆内裂谷的构造环境,是华北克拉通南缘对哥伦比亚超大陆裂解事件的响应。

华北克拉通南缘角子山花岗岩的锆石U-Pb定年、岩石地球化学特征及构造背景

角子山岩基是秦岭造山带东端伏牛山余脉规模居第二位的燕山期侵入岩,其岩石成因模型有助于深入认识华北克拉通南缘伏牛山余脉早白垩世酸性岩浆的形成规律和深部构造演化。角子山花岗岩体LA-ICP-MS锆石U-Pb定年样品的30个测点中,18个有效锆石测点的U-Pb年龄集中于(129.5±1.4)Ma(1个)和(116.1±1.4)~(122.2±1.3)Ma(17个)两组,形成了锆石年龄谱,后者的加权平均年龄为(119.3±0.9)Ma。结合前人10个有效锆石测点的U-Pb年龄数据,27颗锆石的加权平均年龄为(118.2±1.2)Ma,代表了角子山花岗岩的形成时代。角子山花岗岩样品具有富Si和碱、贫Ca和Mg的特征,为高钾钙碱性系列岩石,属于准铝质-弱过铝质花岗岩。在微量元素蛛网图中,角子山花岗岩样品显示了Rb、Th及Zr、Hf的正异常和Sr、P、Ti的负异常。角子山花岗岩稀土总量为20.9×10^(-6)~204×10^(-6),(La/Yb)N值为4.24~21.0,δEu值为0.53~0.78,稀土配分模式呈轻稀土富集(右倾平滑)和中、重稀土亏损(近水平)的特征。角子山花岗岩样品的LaN-(La/Yb)N投点显示了正相关关系,表明其成分变异受控于部分熔融作用。角子山花岗岩的部分熔融源残余相包括角闪石、斜长石和金红石,无石榴子石残余,表明它形成于正常厚度地壳,存在深度大致为40~50 km和小于30 km的两个部分熔融岩石源区。角子山花岗岩形成于秦岭早白垩世陆(板)内造山阶段,经历了岩浆/流体混合再活化作用,是~120 Ma区域岩石圈拆沉作用的产物。

内蒙古喀喇沁旗大西沟萤石矿床成因:来自稀土元素、流体包裹体和H-O同位素的制约

萤石是战略性矿产,对于维护国家资源安全和经济稳定发展具有重要作用。内蒙古喀喇沁旗位于华北板块北缘,是萤石矿的重要产区,笔者对喀喇沁旗大西沟萤石矿床进行了稀土元素、流体包裹体和H-O同位素分析,探究其成矿流体性质及矿床成因。大西沟早阶段萤石稀土元素含量高于晚阶段萤石,早、晚阶段萤石具有相近的Y/Ho值,指示其同源性,在Tb/Ca-Tb/La图解中,样品全部落入热液矿床范围内,指示矿床为热液成因。早、晚阶段萤石均具有Eu的负异常和Ce的弱负异常,说明其形成于还原环境。萤石中流体包裹体类型以富液相的气液两相包裹体为主,均一温度集中于160~190℃,盐度集中于0.18%~2.57%NaCl_(eqv),密度集中于0.88~0.94 g/cm^(3),综合区域萤石矿床的H-O同位素数据,单一型萤石矿床的H-O同位素组成具有明显的纬度效应,指示成矿流体以大气降水为主。大西沟萤石矿床为中低温热液脉型矿床,根据矿脉穿插关系,推断大西沟萤石矿床形成于燕山晚期(<120 Ma),晚侏罗世和早白垩世两期韧性构造变形形成的大量断层和裂隙为成矿流体运移和聚集提供通道,水岩作用是萤石的主要沉淀机制。

河北张三营碱长花岗岩铌铁矿族矿物特征及其意义

张三营碱长花岗岩位于华北克拉通北缘,岩体具高分异特征,整体富铌,具有一定的成矿潜力。为查明其含铌矿物种类及岩浆演化过程,本文对岩体中铌铁矿族矿物开展了显微结构和矿物化学研究。结果表明:铌铁矿族矿物是碱长花岗岩中最主要的含铌矿物,化学成分富铌(Nb)、贫钽(Ta),以铌铁矿为主,少量为铌锰矿,按成因分为岩浆期和岩浆—热液期两类。岩浆期铌铁矿族矿物数量多,矿物多自形且具振荡环带结构,推测结晶于岩浆过程;背散射电子图像中少量岩浆期铌铁矿族矿物出现“亮边”结构和成分反环带,暗示矿物受熔体交代作用影响。岩浆—热液期铌铁矿族矿物含量较少,化学成分均匀,Mn^(#)和Ta^(#)值相对较高,是从熔体中快速沉淀形成的。张三营碱长花岗岩岩浆演化经历了岩浆冷凝期、岩浆—热液过渡期和热液期。岩浆冷凝期历时较长,是岩体富铌的关键,岩浆—热液过渡期熔体对铌、钽富集起到一定的作用,热液期流体交代作用较弱,影响有限。

Sinian hydrocarbon accumulation conditions and exploration potential at the northwest margin of the Yangtze region, China

Based on outcrop, drilling, logging and seismic data, the reservoir forming conditions, reservoir forming model and exploration potential of the ultra-deep Sinian Dengying Formation at the northwest margin of Yangtze craton region were examined.(1) This area is in craton rifting stage from Sinian to Early Cambrian, characterized by syn-sedimentary faults and rapid subsidence, significant sedimentary differences, and development of Dengying Formation platform margins on both sides of the rift.(2) The Sinian–Cambrian in this area has two sets of high-quality source rocks, Doushantuo Formation and Maidiping-Qiongzhusi Formation;of which, the latter has a thickness of 150–600 m and hydrocarbon generation intensity of(100-200)×10;m;/km;.(3) The mounds and shoals in the platform margin of Sinian Dengying Formation controlled by faults are thick and distributed in rows and zones;they are reformed by contemporaneous–quasi-contemporaneous and supergene karstification jointly, forming pore-type reservoirs with a thickness of 200-400 m.(4) The two sets of source rocks enter oil generation windows from Permian to Early Triassic, and the oil migrates a short distance to the lithologic traps of mounds and shoals to form a huge scale paleo-oil reservoir group;from Late Triassic to Jurassic, the oil in the paleo-oil reservoirs is cracked into gas, laying the foundation of present natural gas reservoirs.(5) The mound-shoal body at the platform margin of Dengying Formation and the two sets of high-quality source rocks combine into several types of favorable source-reservoir combinations, which, with the advantage of near-source and high-efficiency reservoir formation, and can form large lithologic gas reservoirs. The Mianyang-Jiange area is a potential large gas field with trillion cubic meters of reserves. According to seismic prediction, the Laoguanmiao structure in this area has the Deng-2 Member mound-shoal reservoir of about 1300 km^(2), making it a ultra-deep target worthy of exploration in the near future.