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Weichanglu, China

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

Liu Y.,China University of Geosciences | Deng J.,China University of Geosciences | Wang Z.,China University of Geosciences | Zhang L.,China University of Geosciences | And 4 more authors.
Acta Petrologica Sinica

The Jiaodong Peninsula, the most important gold province in China, is an important part of the Pafic Rim Mesozoic-Cenozoic gold mineralization area, where the Mesozoic granitoids are widespread. The majority of gold resources (>95%) in Jiaodong Peninsula are hosted by the Late Jurassic Linglong and Early Cretaceous Guojialing granitoids. However, there is still controversy over the petrogenesis and sources of the granitic rocks, especially the Early Cretaceous granitoids. The Xincheng gold deposit, located in the northern part of the Jiaojia fault in northwestern Jiaodong Peninsula, is the only large gold deposit with a proven reserve of >200t Au hosted by the Early Cretaceous granitoids until now. As the host rocks of the Xincheng gold deposit, the Xincheng granitoids comprise an inner medium-to fine-grained quartz monzonite and an outer medium-to coarse-grained porphyritic-like monzogranite, which emplaced at 127 ∼ 132Ma. A new phase with smaller granular size, minor phenocrysts, but more felsic composition was found based on further geological observations, which is completely different from medium-to coarse-grained porphyritic-like monzogranite. In this paper, it was defined as medium-to fine-grained porphyritic-like monzogranite. This paper systematically investigated the medium-to fine-grained porphyritic-like monzogranite, and conducted LA-ICP-MS zircon U-Pb dating, major and trace elements geochemical, and Lu-Hf isotopic constitution. These data enable us to discuss the petrologic classification, forming age, source region of medium-to finegrained porphyritic-like monzogranite, and the relationship between it and the Xincheng granitoids. The medium-to fine-grained porphyritic-like monzogranites, possess high SiO2(71. 18% -73.72%), total alkalis (K2O + Na2O =7. 07% - 8.64%), Ba (>793 ×10-6), Sr(>729×10-6) and LREE (>71.14 × 10-6), with low Al2O3(13. 57% - 15.73%), MgO (0.22%-0.385%), Rb (<91.7×10-6), Th (<7.41 × 10-6), U (<4. 51 × 10-6), Nb (<4.49× 10-6), Ta (<0.263 × 10-6), Y(<3.67 × 10-6) and HREE (<3. 928 × 10-6). The rocks are characterized by no significant Eu anomalies and prominent depletion of Nb, Ta, P, Ti. All these results indicate that the rocks belong to the high Ba-Sr granites. LA-ICP-MS zircon dating yields U-Pb age of 123 ± 1Ma for the medium-to fine-grained porphyritic-like monzogranites. Regarding to the previous geochronological data (127 ± 2Ma - 132 ± 1Ma) for medium-to fine-grained quartz monzonite and medium-to coarse-grained monzogranites, and similar major elements compositions, REE and trace element distribution patterns among these three kinds of rocks, it is suggested that the Xincheng granitoids were emplaced at 123 ± 1 Ma - 132 ± 1 Ma. The medium-to fine-grained porphyritic-like monzogranites have zircon εHf(t) values of - 20. 76 to -18. 66, and two-stage Hf model ages (tDM2) vary in range of 2351 ∼2479Ma. In the εHf(t) vs. Age diagram, all the data points lie below the chondritic Hf evolution line, indicating that the ancient crust was an important source for the Xincheng granitoids. Previous zircon Hf isotope data obtained from quartz monzonite, medium-to coarse-grained monzogranites and the Linglong granite, along with presence of two Archean (2629 ± 14Ma, 2402 ± 18Ma) and three Mesozoic (150 ± 7Ma, 151 ± lMa, 147 ± lMa) inherited zircons, indicate that the monzogranites might be generated by partial melting of Precambrian metamorphic basement rocks of coupled with assimilation of the wall rocks of the upper crust, especially the Late Jurassic Linglong granites. Source

Yang L.,China University of Geosciences | Deng J.,China University of Geosciences | Wang Z.,China University of Geosciences | Zhang L.,China University of Geosciences | And 3 more authors.
Acta Petrologica Sinica

Jiaodong Peninsula is the most important gold concentration area of China, more than 150 gold deposits within it have been found and the proven gold reserves add up to 4000 tons. The amount of gold deposits and gold resource are huge, gold occurrence and mineralization type vary with the widely distributed gold deposits, however, the metallogenic geodynamics background, ore-host rock environment, gold occurrence conditions and metallogenic characteristics are identical as a whole: (1) Jiaodong area is an endogenic hydrothermal gold concentration area consisting of Precambrian base rocks and ultra-high pressure (UHP) metamorphic rocks, tectonism and magmatism happened frequently in Mesozoic, 130 ∼ 110 Ma gold metallogenic events occurred 2000Myr or so later than the regional metamorphism; (2) regional gold metallogenic system formed in the Early Cretaceous continental-margin extension tectonic background, large-scale gold metallogenic events happened in the process of regional NW extension changing to NE extension followed by the NEE compression, which corresponded to the lithosphere reduction in East China, North China craton destruction and the peak of continental rifting; (3) gold deposits clustered around the NNE Linglong, Queshan and Kunyushan metamorphic core complexes, mainly along the regional NE-NNE detachment faults developing along the contact zone of Precambrian metamorphic rocks and Mesozoic granites; (4) the ore-controlling fault belts went through the early ductile-brittle deformation and late brittle deformation structure superposition, extended in smooth-out waveforms in 3D space and controlled the lateral trending and subsection enrichment of gold orebodies; (5) the mineralization types mainly include clastic altered (breccia) rock type, (sulfide-) quartz vein type and compound vein-belt type, textures like the crush texture, crystalline-granular texture, interstitial texture and structures like the disseminated structure, vein structure, massive structure, crumby structure are abundant in the ore rocks, which indicates the ore-forming environment changed from ductile-brittle conditions to brittle conditions; (6) metallic minerals mainly include pyrite, chalcopyrite, galena and sphalerite, non-metallic minerals mainly include quartz, sericite, potash-feldspar and calcite; gold minerals mainly include the electrum, natural gold and a small amount of küstelite, which mainly occur in the fractures of pyrites and quartz in the form of visible gold, lesser in crystal gap and as inclusions; hydrothermal alteration types mainly include pyritization, silicification, sericitization and carbonatation; ore-forming elements mainly consist of the Au-Ag (-Cu-Pb-Zn) assemblage; the alteration and mineralization assemblage mentioned above show the characterisics of mesothermal-epithermal assemblage; (7) ore-forming fluids came from both the crust and mantle and are mainly the crust source metamorphic fluids; metallogenic materials derived from the Precambrian metamorphic basement rock mass which reactivated in the Mesozoic, mingling with a small amount of the shallow crustal and mantle components. The consistency of regional metallogenic characteristics indicate that the Early Cretaceous large-scale gold metallogenesis in Jiaodong gold concentration area is controlled by the uniform geological events, and the gold metallogenesis belongs to an epigenetic mesothermal-epithermal hydrothermal vein gold metallogenic system. These gold deposits have obvious characteristic of spatio-temporal cluster distribution and lie mainly along the contact zones of different lithofacies around three metamorphic core complexes. From west to east, the gold mineralization age changes from older to newer. Therefore, three gold subsystems can be divided, which are the altered rock-quartz vein type in Jiaobei Uplift, the sulfide-quartz vein type in Sulu UHP metamorphic belt and the altered breccia type in north margin of Jiaolai Basin. The mineralization style changes from disseminated-veinlet, veinlet-stockwork and quartz vein type, to sulfide-quartz vein type, to altered breccia type. The texture and structure of ores are characterized by veinlet-disseminated structure dominated, to band structure and comb structure, and then to breccia structure, indicating mineralization occurred respectively in brittle-ductile transformation zone (ca. 15km deep), a brittle extension-shear fault zone, and a brittle breccia zone (ca. 5km deep). The decrease of the size and strength of alteration and mineralization, and the increase of shallow crustal components in metallogenic materials, may be related to the deposits' location which is more and more far away from the source area. The ore-forming P-T conditions gradually decreased and the meteoric water and/or basin brine ratio in the ore-forming fluid gradually increased, respectively, which corresponds to the shallower metallogenic depth and more and more extended trending mineralization tectonic environment. All the regional regular changes of metallogenic characteristics reflect a crustal continuum metallogenic in different vertical depth of crust, between the detachment fault ductile-brittle transition zone and the brittle breccia zone. Mesozoic gold metallogenic system of the Jiaodong gold province is distinct from typical "intrusion-related gold deposit", "orogenic gold deposit" or other known gold deposit type around the globe, and can't be classified into the known metallogenic model. To reasonably explain the unique geodynamic background, environment of ore-host rock and mineralization characteristics, we put forward the new understanding of the "Jiaodong type" gold deposit and metallogenic model. We conclude that the rollback of ancient Pacific Izanagi subduction plate may be the main drive mechanism leading to large-scale revitalizing of the metallogenic materials in regional Precambrian metamorphic basement rock mass, and ore-forming fluids mainly came from metamorphic dehydration of the subducting plate. Gold is mainly in Au (HS)2 -complex and transported along detachment fault system in ore fluids. The tectonic space increases sharply as well as the metallogenic temperature and pressure decreases suddenly around the brittle-ductile transformation zone of detachment fault system and brittle breccia zone. Therefore, CO2and H2S lossing from the ore fluids and sulfidation leads to a stability decreasing of Au(HS)2 -and other gold complexes, and subsequent large-scale gold precipitation. Source

Yang L.-Q.,China University of Geosciences | Deng J.,China University of Geosciences | Wang Z.-L.,China University of Geosciences | Guo L.-N.,China University of Geosciences | And 6 more authors.
Economic Geology

The Xincheng gold deposit, hosted by the Early Cretaceous 132 to 123 Ma Guojialing-type granitoids in northwest Jiaodong Peninsula, southeast North China craton, formed about 2 billion years later than regional metamorphism of the Archean Jiaodong basement rocks. The Xincheng deposit comprises mineralized zones with three types of hydrothermal pyrite associated with gold, tellurides, and a variety of sulfides: py1 as disseminated euhedral to subhedral grains in altered granitoids around quartz veins; py2 as subhedral grains with brittle cataclastic textures and fractures in quartz-pyrite veins; and py3 as subhedral, partially corroded crystals in sulfide-rich veins or veinlets. All three generations of pyrite are unzoned and have low trace element contents, including very low lattice-bound gold contents: (py1: 0.180 ppm; py2: 0.053 ppm; py3: 0.060 ppm). Given that there is 10 to 15% pyrite in the ore zone at Xincheng, its very low gold content indicates that it contributes >0.2% of gold to the 7.75 g/t gold in the orebody. Instead, over 99% of the gold is present as discrete electrum and/or gold (total range 0.02-59% silver) grains, which are largely sited in fractures at all scales in pyrite, other ore minerals, and quartz. Importantly, visible gold in py3 is also sited on solution-corroded pyrite grains. The pyrite textural and geochemical data indicate that it is impossible to derive the high gold-grade orebodies through local remobilization of originally lattice-bound gold in pyrite. Instead, the gold is interpreted to have been deposited through sulfidation reactions and phase separation of a H2O-CO2 ore fluid during progressive brittle cataclastic deformation associated with seismic activity and regional sinistral transtensional shear movement. This concomitant fluid infiltration and deformation caused episodic deposition and fracturing and corrosion of earlier formed pyrite and deposited visible gold in dilational cracks. The coupled development of the transtensional, rather than normal transpressional setting, and precipitation of gold within dilational veins and wall-rock alteration facilitated the deposition of visible gold and an exceptionally high gold tenor. All deposit characteristics indicate that the Xincheng gold deposit is a member of the epizonal orogenic deposit class. © 2016 by Economic Geology. Source

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