Deep Structural Framework and Genetic Analysis of Gold Concentration Areas in the Northwestern Jiaodong Peninsula, China： A New Understanding based on High-Resolution Reflective Seismic Survey

The gold concentration areas in the northwestern Jiaodong Peninsula constituted an important gold metallogenetic region in Eastern China during the Mesozoic. The deep geological bodies' texture characteristic is important for exploring the resources thoroughly and understanding the metallogenic process. The detailed textures were revealed using high-resolution seismic profiles through the three major ore-controlling structures-Sanshandao fault zone, Jiaojia fault zone and Zhaoping fault zone. This study aims to establish a deep structural framework of this area. Based on their formation mechanism, the fault structures developed in the area can be divided into regional and local fault structures. The structural styles are characterised by superimposing their compressional, strike-slip and extensional multi-stage activities. The crust is cut by vertical structures corresponding to a left-lateral strike-slip fault system on the surface. Nearby these structures are the arc-shape structures formed by multi-stage magma intrusions into the upper crust. Bounded by the Tancheng–Lujiang and Muping–Jimo fault zones, the current Jiaodong block, developed a series of NE-trending strike-slip fault systems, was probably formed by the assemblage of several obliquely aligned blocks. The intensive magmatism and hydrothermal activity between the blocks induced large-scale mineralisation. It provides a new angle of view for understanding the cratonic destruction and large ore-concentration formed during the Mesozoic.

Petrological and Geochemical Constraints on the Origin of Strongly Peraluminous Granitoids from the Triassic Guangtoushan Pluton in South Qinling

As an important part of the early Mesozoic granites in the South Qinling tectonic belt(SQTB),the Guangtoushan pluton provides a material basis for research on the composition of magma sources and the effects of peritectic assemblage entrainment(PAE)on the changes in the granite composition.As shown by the results of LA-ICP-MS zircon U-Pb dating,the Guangtoushan pluton was emplaced during the Late Triassic(214-212 Ma)and was formed in the post-collision stage between the SQTB and the Yangtze plate.The collected samples had high SiO_(2)content and low Cr and Ni contents,indicating that the magmas did not undergo significant crust-mantle mixing during their evolution.The Guangtoushan granitoids were distributed along the trend line of magmatic fractional crystallization in the F-An-Or diagram.This result,combined with the relatively homogeneous Sr-Nd isotopic composition,implies that the Guangtoushan pluton underwent slight assimilation and contamination.As can be inferred from the comparison between the compositions of the Guangtoushan granitoids and various fluid-absent experimental melts,the magma sources of the Guangtoushan granitoids contain a variety of materials,such as graywackes,pyroclastic graywackes,and pelites and are not derived from lower crustal mafic rocks.The correlation between the maficity and the major and trace elements further indicates that the strongly peraluminous granitoids from the Guangtoushan pluton was formed by the partial melting of biotite-bearing crustal rocks and its magmatic evolution was accompanied by the entrainment of clinopyroxenes and accessory minerals.

Deep gold mineralization features of Jiaojia metallogenic belt,Jiaodong gold Province:Based on the breakthrough of 3000 m exploration drilling

Recently,continuous breakthroughs have been made about deep gold prospecting in the Jiaodong gold province area of China.Approximately 5000 t of cumulative gold resources have been explored in Jiaodong,which has thus become an internationally noteworthy gold ore cluster.The gold exploration depth has been increased to about 2000 m from the previous<1000 m.To further explore the mineralization potential of the Jiaodong area at a depth of about 3000 m,the Shandong Institute of Geological Sciences has drilled an exploratory drillhole named“Deep drillhole ZK01”to a depth of 3266 m.Hence,as reported herein,the mineralization characteristics of the Jiaojia metallogenic belt have been successfully documented.ZK01 is,to date,the deepest borehole with an gold intersect in China,and constitutes a significant advance in deep gold prospecting in China.The findings of this study further indicate that the depth interval of 2000 m to 4000 m below the ground surface in the Wuyi Village area incorporates 912 t of inferred gold resources,while the depth interval of 2000 m to 4000 m below the surface across the Jiaodong area possesses about 4000 t of inferred gold resources.The Jiaojia Fault Belt tends to gently dip downward,having dip angles of about 25°and about 20°at vertical depths of 2000 m and 2850 m,respectively.The deep part of the Jiaojia metallogenic belt differs from the shallow and moderately deep parts about fracturing,alteration,mineralization,and tectonic type.The deep zones can generally be categorized from inside outward as cataclastic granite,granitic cataclasite,weakly beresitized granitic cataclasite,beresitized cataclasite,and gouge.These zones exhibit a gradual transitional relation or occur alternately and repeatedly.The mineralization degree of the pyritized cataclastic granite-type ore in the deep part of the Jiaojia metallogenic belt is closely related to the degree of pyrite vein development;that is,the higher the pyrite content,the wider the veins and the higher the gold grade.Compared to the shallow gold ores,the deep-seated gold ores have higher fineness and contain joseite,tetradymite,and native bismuth,suggesting that the deep gold mineralization temperature is higher and that mantle-sourced material may have contributed to this mineralization.ZK01 has also revealed that the deep-seated ore bodies in the Jiaojia metallogenic belt are principally situated above the main fracture plane(gouge)and hosted within the Linglong Granite,contradicting previous findings indicating that the moderately shallow gold ore bodies are usually hosted in the contact zone between the Linglong Granite and Jiaodong Group or meta-gabbro.These new discoveries are particularly significant because they can help correct mineralization prospecting models,determine favorable positions for deep prospecting,and improve metallogenic prediction and resource potential evaluation.

A Textural and Mineralogical Study of the Shanzhuang Banded Iron Formation, Southeastern Margin of the North China Craton: Implications for the Overprint History of Hydrothermal Alteration and Supergenesis after Mineralization

The newly discovered Shanzhuang BIF is hosted in the Shancaoyu Formation of the Taishan Group within the Eastern Block,southeastern margin of the North China Craton.The ores can be subdivided into three types in terms of mineral assemblages,corresponding to three types(Ⅰ,Ⅱ,Ⅲ).The element concentration of the type Ⅰ magnetite is similar to that of the type Ⅱ magnetite,while the type Ⅲ magnetite is similar to that of the schist.In general,magnetite and hemat ite grains from the ores show high concentrations of Mn(1317,1162 ppm),Co(787,1023 ppm),Al(2224,2435 ppm)and Ti(540,300 ppm),Whereas magnetite is depleted in Si(420 ppm)and hematite enriched in Si(1690 ppm).Detailed petrographic and mineral chemical analysis of magnetite,hematite,amphibole/hornblende and pyroxene,reveals that almost all the minerals occur as subhedral-anhedral grains with pits and fractures,and the BIF is recrystallized to metamorphic assemblages of high amphibolite facies.Hornblende is highly enriched in Fe,Mg and Ca,but depleted in K and Na,mostly belonging to magnesiohornblende.In addition,the ratios of Mg/(Mg+Fe^2+),Fe^3+/(Fe^3++Fe^2+),Si/(Si+Ti+Al)and Al/Si are 0.48-0.64,0.17-0.36,0.79-0.88 and 0.14-0.27,respectively.It is suggested that hornblende is neither a typical magmatic origin nor a typical metamorphic.Pyroxene has the characteristics of high Ca and Fe,but low Ti and Al,with end-member components En,Wo and Fs in the ranges of 25.22-28.64 wt%,43.71-46.40 wt%and 24.51-27.62 wt%,respectively,belonging to clinopyroxene,and mostly diopside,might be formed during the prograde metamorphism in the absence of H2 O.The carbonate such as dolomite-ankerite series is probably a precursor mineral of the BIF deposit.Mass mineral chemical and structural characteristics indicate that the Shanzhuang iron deposit has been subjected to varying degrees of oxidized hydrothermal superimposed reformation,metamorphism,and supergenesis after mineralization,during which some elements have been migrated in some degree.

Cooling History of Mesozoic Magmatism and Implications for Large-Scale Gold Mineralization in the Jiaodong Peninsula, East China: Constraints from T-t Paths Determined by U-Pb Thermochronology of Zircon and Apatite

The Mesozoic intrusions of the Jiaodong Peninsula,eastern China,host giant gold deposits.Understanding the genesis of these deposits requires the determination of the source of the parental auriferous fluid and the timing of gold mineralization,which are strongly influenced by the cooling/uplift histories of the hosting intrusions.We performed an integrated U-Pb geochronology study on both zircon and apatite from four major magmatic episodes of the Jiaodong Peninsula.The zircon and apatite U-Pb ages are 156.9±1.2 and 137.2±2.4 Ma for the Linglong intrusion,129.9±1.0 and 125.0±3.8 Ma for the Qujia intrusion,119.5±0.7 and 117.2±1.8 Ma for the Liulinzhuang intrusion,118.6±1.0 and 111.6±1.6 Ma for the Nansu intrusion,respectively.The coupled zircon and apatite data of these granitoids indicate a slow cooling rate(11.9°C/Ma)in the Late Jurassic,and rapid uplift and cooling(35.8-29.2°C/Ma)in the Early Cretaceous.The dramatically increased uplift and cooling period in the Early Cretaceous are contemporaneous with large-scale gold mineralization in the Jiaodong Peninsula.This implies that thermal upwelling of asthenosphere and related tectonic extension played an important role in gold remobilization and precipitation.

He–Ar Isotopic Tracing of Pyrite from Ore-forming Fluids of the Sanshandao Au Deposit, Jiaodong Area

The Sanshandao Au deposit is located in the famous Sanshandao metallogenic belt,Jiaodong area.To date,accumulative Au resources of 1000 t have been identified from the belt.Sanshandao is a world-class gold deposit with Au mineralization hosted in Early Cretaceous Guojialing-type granites.Thus,studies on the genesis and ore-forming element sources of the Sanshandao Au deposit are crucial.He and Ar isotopic analyses of fluid inclusions from pyrite(the carrier of Au)indicate that the fluid inclusions have 3 He/4 He=0.043–0.21 Ra with an average of 0.096 Ra and 40 Ar/36 Ar=488–664 with an average of 570.8.These values represent the initial He and Ar isotopic compositions of ore-forming fluids for trapped fluid inclusions.The comparison of H–O isotopic characteristics combined with deposit geology and wall rock alteration reveals that the ore-forming fluids of the Sanshandao Au deposit show mixed crust–mantle origin characteristics,and they mainly comprise crust-derived fluid mixed with minor mantle-derived fluid and meteoric water during the uprising process.The ore-forming elements were generally sourced from pre-Cambrian meta-basement rocks formed by Mesozoic reactivation and mixed with minor shallow crustal and mantle components.

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.

A Research of the Cretaceous-Paleogene Boundary in the Pingyi Basin, Shandong Province

The Bianqiao Formation (in the Pingyi Basin, Shandong Province, China) is a typical set of continuous lacustrine carbonate deposits during the Cretaceous-Paleogene period, which is considered as an ideal stratigraphic unit for KPB research. This study is based on the borehole PYZK01, which is located at Tongjiazhuang village in Bianqiao Town of Pingyi country. According to biostratigraphy research, the Bianqiao Formtion establishes one charophyte assemblage: Porocharaanluensis-Charayuntaishanensis var. acuta-Turbocharaspecialis, and one sporopollen assemblage: Deltoidosporaadriensis-Rugubivesiculites- Schizaeoisporites. This result indicates that the stratigraphic age during 0 - 12.25 m is the Paleogene, 37.8 m - 60 m is the Late Cretaceous, and 12.25 - 37.8 m is a transition stage from the Late Cretaceous to the Paleocene. By geochemical study, it was established carbon and oxygen isotopic strata in the drill. Through the magnetostratigraphy research, we find eight positive polarity zones and seven reversed polarity zones, build the magnetic polarity sequences of the borehole, and propose a contrast scheme with the international standard magnetic polarity time column. After comprehensive discussion, it is preliminarily believed that the Cretaceous-Paleogene boundary is located at the depth of 31.98 m in PYZK01, namely, in the first section of the Bianqiao Fm.

Paleogene Tectonic Evolution Controls on Sequence Stratigraphic Patterns in the Central Part of Deepwater Area of Qiongdongnan Basin, Northern South China Sea

In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift succession in Qiongdongnan Basin, northern South China Sea, was built using seismic profiles, complemented by well logs and cores. One first-order and three second-order sequences were identified on the basis of basin-scale unconformities, and seven third-order sequences are defined by unconformities along the basin margins and correlative conformities within the central basin. Through unconformity analysis and backstripping procedure, the Paleogene synrift tectonic evolution of deepwater area of Qiongdongnan Basin was proved to be episodic, which can be divided into rifting stage-I, rifting stage-II and rifting stage-III. Episodic rifting resulted in the formation of various types of structural slope break belts, which controlled different architectures and internal makeup of sequences. This study enhances the understanding of the control of tectonic evolution on sequence stratigraphic patterns and establishes relevant patterns in a typical rift basin, and further proposes the favorable sandstone reservoirs developing in different sequence stratigraphic patterns, which will be pretty helpful for subtle pool exploration in deepwater area of petroliferous basins.