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Weichanglu, China

Zhang B.,China University of Geosciences | Yang L.,China University of Geosciences | Huang S.,Jiaojia Gold Company | Liu Y.,China University of Geosciences | And 5 more authors.
Acta Petrologica Sinica

Jiaodong Peninsula, the most important gold province in China, is an area with concentration occurrence of large-superlarge gold deposits, the proved reserves in Jiaodong Peninsula account for nearly 1/3 of the country's. Fracture zone altered type gold deposit is the most important deposit type which accounts for more than 90% of the proved gold reserves in Jiaodong Peninsula. Jiaojia gold deposit is named after "Jiaojia-type" fracture zone altered rock type gold deposit, large-scale sericite-quartz alteration zone (with the width of 20 ∼200m) and potassic alteration zone (with the width of 50 ∼300m) occur in the gold deposit. Altered rock type gold orebody mainly develops in the sericite-quartz alteration zone which is in the footwall of Jiaojia fault zone. Based on the detailed geologic observations in the field, this paper found out the alteration type and mineral assemblage of the Jiaojia gold deposit, collected different types of alteration rock samples scientifically, and conducted rock geochemistry element analysis which uses the method of the mass balance to discuss the regularity of elements migration in the hydrothermal alteration process and mechanism. Thereinto, potassic alteration occurs in the premineralization, potassic granite is usually as lumpy and breccia residual in the pyrite-sericite-quartz and sericite-quartz altered rock which is controlled by the secondary faults in the footwall of the Jiaojia fault, and the scale is controlled by the faults. The scale of sericite-quartz altered rock is the largest in the footwall of the Jiaojia fault with the width of 10 ∼ 200m, sericite-quartz altered zone controlled by secondary faults is relatively small, usually presenting as wide 0. 1 ∼ 1 m veins in the potassic granite, which indicates sericite-quartz alteration is later than potassic alteration. Compared with biotite granite, rocks from various alteration zones show high contents of K2O and low contents of A12O3, CaO and Na2O, but elements like Si, Fe, and Mg have different characteristics. Potassic granite are rich in K2O, while both sericite-quartz altered rock and pyrite-sericite-quartz altered rock are characterized with increasements of MgO and Fe2O3. During the process of potassic alteration, SiO2and K2O were added, indicating that the forming fluid is silicon-rich, alkaline and oxidation. In the process of alteration from potassic granite to pyrite-sericite-quartz altered rock, the Fe2O3increased obviously, which may be caused by the decomposement of biotite and other melanocratic minerals. Furthermore, sulfophilic elements like Au, Ag, As, Pb and Zn also increased significantly. Part of the gold may be derived from Linglong biotite granite. In the process of potassic alteration, the metasomatism between the wall rock and silicon-rich, alkaline and oxidation fluids, extracted gold in the form of high valence ion from wall rocks. To be specific, dispersed reduced gold (Au0) was activated to be oxidized (Au+, Au3+), and migrated with the fluids in the form of AuH3SiO4. In the process of sericite-quartz alteration, the descent of the content of SiO2induced the decomposement of AuH3SiO4. Fe2+and Fe3+were consumed to form the pyrites, which induced the deposition and enrichment of gold. Gold activate, migrate and deposit run through all these process. Source

Wang Z.,China University of Geosciences | Zhao R.,Jiaojia Gold Company | Zhang Q.,Xincheng Gold Company | Lu H.,Xincheng Gold Company | And 2 more authors.
Acta Petrologica Sinica

The majority of gold resources (>95%) in the Jiaodong Peninsula, the largest gold producer in China, are hosted in the Late Jurassic Linglong-type and Early Cretaceous Guojialing-type granitoids. However, the petrogenesis and sources of the granitic rocks, especially the Early Cretaceous granitoids, remain controversial. The Guojialing-type granitoid, intruding the Linglong-type granitoid, includes six plutonic bodies from west to east through the Jiaodong Peninsula: Sanshandao, Xincheng, Shangzhuang, Beijie, Congjia and Guojialing, of which the Xincheng pluton is the only Guojialing-type granitoid that hosts the super-large gold deposit in Jiaodong. The Xincheng pluton, intruding the Linglong biotite-granite, mainly consists of quartz monzonite and monzogranite. The boundary between the quartz monzonite and monzogranite is unclear, suggesting that they are coeval intrusions. In order to discuss the petrogenesis of the Xincheng Early Cretaceous granitoids, and reveal the geodynamics back ground for the high Ba-Sr Guojialing-type granite, this paper systematically investigated the Xincheng pluton to sample the monzogranite, and conducted the elemental, mineralogical and Sr-Nd isotopic analyse. The Xincheng monzogranites, typical high Ba-Sr granites, possess high SiO2(70. 89% ∼ 73.35%), K2O (7.03% -8.68%), total alkalis (K2O+Na2O =7. 03% -8.68%), Sr (>640 × 10-6), Ba (> 853 × 10-6) and LREE (>65.43 × 10-6), with low HREE and HFSE contents and insignificant Eu anomalies. The rocks display markedly high Sr/Y (> 115) and (La/Yb)N(20. 32-198.8) ratios. They have low Al2O3(14.41% -15.54%), MgO (0.21% -0.62%), Rb (<103 × 10-6), Th (<10. 3 × 10-6), U (>5. 87 × 10-6), Nb (<6. 14 × 10-6), Ta (<0.599 × 10-6), Y (< 10. 3 × 10-6) and HREE (δ. 3 × 10-6). The plagioclases and K-feldsparsin the monzogranites both show the reverse zoning texture, of which the plagioclases belong to oligoclase with An contents of 12. 87-22. 91, and the K-feldspars belong to orthoclase with Or contents of 81. 24-93. 69. The monzogranites have 87Sr/86Sr (ISr) and εNd(t) values of 0. 71071-0. 71172 and -21.3 ∼ - 17.1, respectively, with the two-stage Nd model ages (tDM2) of 2310 ∼2648Ma. Detailed elemental, mineralogical and Sr-Nd isotopic data suggest that the Xincheng monzogranites were most likely generated by partial melting of the basement rocks of the Jiaobei terrane with minor addition of intermediate magma which were partial melting of juvenile mafic lower crust formed by the earlier underplating of mantle magma. Their genesis is linked to asthenosphere upwelling, triggered by the subduction of the paleo-Pacific slab beneath the North China Craton. Source

Li R.,China University of Geosciences | Liu Y.,China University of Geosciences | Li H.,China University of Geosciences | Zheng X.,Shandong Gold Mining Stock Co. | And 2 more authors.
Acta Petrologica Sinica

Xincheng gold deposit is a typical "Jiaojia" type alteration rock type deposit within cataclastic zone, in that orebodies shape and scale bend to structural control, which is ideal region to do research on ore-controlling deformation environment of the complex structure-fluid coupling metallogenic system. The tectonite in the cataclastic fault zone not only are the hosts of deformation behavior, but also are response for environment of structure deformation. Thus, this paper is based on the detailed structure analysis of the outcrop, collected oriented samples scientifically in the cataclastic zone in Xincheng gold deposit, and conducted microstructure and EBSD fabric analysis. The microstructure features of tectonite in Xincheng gold deposit can be divided into ductile deformation and brittle deformation. Ductile deformations consist of undulatrory extinction, banded extinction, quartz subgrain, quartz subgrain rotation recrystallization, boundary migration recrystallization, ribbon structure, σ type porphyroclast system, δ type porphyroclast system, bink bands, deformation lamella, stress-induced lamellae, myrmekite texture, mica fish and mechanical twin. Brittle deformations include bookshelf structure, pressed shear fracture and tension crack. All of the feldspar porphyroclast system, bink bands, deformation lamella, myrmekite texture, mica fish, quartz boundary migration recrystallization and ribbon structure indicate the high temperature ductile deformations are dominant in the pre-mineralization stage. The quartz undulatrory extinction, subgrain, subgrain rotation, bulging recrystallization, calcite mechanical twin, feldspar tension crack show both ductile deformation and brittle deformation are occurrence in the mineralization stage. The pressed shear fractures without filling represent low temperature brittle deformation in the post-mineralization. In combination with EBSD fabric analysis, ore-controlling structure deformation condition of Xincheng gold deposit can be divided into 3 stages. The ductile-brittle sinistral shear deformation occur in pre-mineralization resulted from NW-SE compression, with temperature 600-700°C, differential stress 61. 37 ∼ 111. 09MPa, strain axial ratio measurement a/c 2.295 ∼3.978 and fractal dimension value of the quartz boundary of dynamic recrystallization 1. 466-1.599, which indicates the condition with high temperature, high pressure, high strain zone and strain rate in pre-mineralization. The NW-SE compression converts into NEE-SWW in mineralization, while brittle pressed-shear deformation arises, with temperature 200-500°C, differential stress 65. 91 ∼ 135.68 MPa, strain axial ratio measurement a/c 1. 403 ∼2. 204 and fractal dimension value of the quartz boundary of dynamic recrystallization 1. 321 ∼1. 378, which suggests the condition with low temperature, high pressure, low strain zone and low strain rate in mineralization. The NWW-SEE compression results pressed-shear deformation in post-mineralization, with temperature 150 ∼ 300°C, represents low temperature, low pressure brittle deformation condition. Source

Wang Z.-L.,China University of Geosciences | Yang L.-Q.,China University of Geosciences | Guo L.-N.,China University of Geosciences | Marsh E.,U.S. Geological Survey | And 7 more authors.
Ore Geology Reviews

The Xincheng gold deposit, located in west Jiaodong Peninsula in southeast North China Craton, is a representative mesothermal lode deposit hosted in Late Mesozoic granitoids in Jiaodong. Gold mineralization occurs as disseminated- and stockwork-style ores within the hydrothermal breccias and cataclastic zones controlled by the Jiaojia fault, whereas echelon tensile auriferous veins hosted in the NE- and NNE-trending subsidiary faults cutting the granitoids occur subordinately. According to crosscutting relationships and mineral paragenesis, four paragenetic stages were identified, which are pyrite-quartz-sericite (stage 1), quartz-pyrite (stage 2), quartz-polysulfide (stage 3) and quartz-carbonate (stage 4). Gold was deposited during the quartz-pyrite and quartz-polysulfide stages. On the basis of microthermometry and Raman spectroscopy on fluid inclusions contained within the quartz veins from stages 2 and 3, three types of fluid inclusions were recognized: (1) type 1 H2O-CO2 inclusions that show high temperatures (ca. 260°C), low salinities (2.4-8.9wt.% equiv. NaCl) and variable XCO2 (0.03 to 0.20), (2) type 2 aqueous inclusions with medium temperatures (ca. 220°C) and low to moderate salinities (3.1-13.3wt.% equiv. NaCl); (3) type 3 pure CO2 inclusions with a carbonic phase density of 0.712±0.03g/cm3. Types 1 and 2 inclusions appear in the same growth phase of the quartz grains from the breccias and tensile auriferous veins. These coexisting inclusions are likely formed by fluid immiscibility due to unmixing from a single homogeneous H2O-CO2 parent fluid at trapping P-T conditions of 221 to 304°C (average 261±19°C) and 780 to 2080bar. The fluid immiscibility is interpreted to be initiated by fluid pressure decrease at ca. 300°C. The ore-fluid P-T-X conditions of the Xincheng gold deposit are the same as those for mesothermal deposits. Gold was most probably transported as a Au(HS)2 - complex at Xincheng. Fluid immiscibility over the temperature interval of 221-304°C resulted in significant H2S loss from the hydrothermal solution, thereby reducing Au(HS)2 - solubility with concomitant deposition of gold. The mineralizing process of the granitoid-hosted Xincheng lode-gold deposit is likely related to the fluid immiscibility. © 2014 Elsevier B.V. Source

Huang T.,China University of Geosciences | Yang L.,China University of Geosciences | Liu X.,China University of Geosciences | Li H.,China University of Geosciences | And 4 more authors.
Acta Petrologica Sinica

The Late Jurassic Linglong biotite granite exposed widely in the Jiaobei terrane, was derived by partial melting of the lower crust, with a lot of inherited zircons witnessed multiplethermal events. These inherited zircon grains can provide important clues for the complex crust evolution. Inherited zircons in the Linglong biotite granite are selected for U-Pb dating, trace element and Hf isotopic compositions analysis to explore the crust evolution of the Jiaobei terrane. We recognize that two period of the crustal growth events took place at ∼ 2.9 Ga and ∼ 2.7Ga, and two episodic crust reworking occurred at ∼ 2. 5Ga and 2. 2 ∼ 1. 8Ga, and two distinctively metamorphic events occured at ∼2.5Ga and 1. 95 ∼ 1. 8Ga, respectively. The ∼ 2. 9Ga magmatism was likely generated in an island-arc system, the ∼2. 7Ga magmatic activity was related to partial melting of the lower crustal mafic rocks, and the ∼2. 5Ga magmatic and metamorphic events were linked to the underplating of mantle plumes, contemporanously, the supracrustal sequence of the Jiaodong Group were deposited. The bimodal magmatism formed at ∼ 2.1Ga, suggested a crustal extention event and might be related to rifting, and consequently, the Paleoproterozoic sedimentary rocks of the Jingshan Group and the Fenzishan Group formed. All the Early Precambrian lithological unites in the Jiaobei terrain were metamorphosed during 1. 95 ∼ 1. 8Ga. Since then, there was no tectothermal event until the Permian, but sedimentation occurred at ∼ 1. 7Ga and ∼ 1. OGa, corresponding to the formation of the Zhifu Group and the Penglai Group, respectively. At the end of the Permian, the Yangtze Block subducted northward beneath the North China Craton. The Triassic continent-continent collision between the North China Craton and the Yangtze Block led the Neoproterozoic granites in the northern margin of the Yangtze Block to experience the ultra-high pressure metamorphism, formed the Sulu UHP metamorphic belt, and then the exhumation of UHP metamorphic rocks occurred. The complex composition of inherited zircons from the Linglong biotite granite may indicate that the Precambrian rocks were involved in the continental collision events and were recycled. Source

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