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    SHRIMP U-Pb zircon geochronology of granitoids fromDongping area, Hebei Province, China constraints on tectonicevolution and geodynamic setting for gold metallogeny [查看] LaichengMiao、YuminQiu、NealMcNaughton、ZhenkuanLuo、DavidGroves、YushengZhai、WeimingFan、MingguoZhai、KangGuan
    The Dongping area in the central part of the northern marginal zone of the North China Craton (NCC) is one of the most important gold-producing areas in China, and has been intruded by a number of alkaline and granitic batholiths or plutons spatially associated with gold deposits. Previous dates on these intrusions yield contradictory data, depending on the isotopic methodology used, and have led to ambiguity in understanding magmatic evolution and gold mineralization of the region.Detailed SHRIMP U–Pb zircon geochronology of the alkaline and granitic rocks in the study area now reveals details of its tectono-magmatic history. Zircons from a granitic gneiss hosting the Xiaoyingpan gold deposit yielded concordant ages of ca.2.5 Ga. This constrains regional metamorphism of the Archaean basement to late Archaean time. A second magmatic event at ca. 1.8 Ga is revealed by xenocrystic/inherited zircons with this age. These two Precambrian events are coeval with those in other parts of the NCC. The largest igneous intrusion in the region, the Shuiquangou syenite–monzonite complex, was emplaced at ca. 390 Ma, as indicated by the magmatic zircon populations of the two samples from the central and eastern parts of the complex. The accretion of a volcanic arc onto the northern margin of the NCC is considered as a plausible cause of this alkaline magmatism. The emplacement of the Guzuizi porphyritic granite pluton at 236F2 Ma represents another major magmatic event in the region, probably a response to postcollisional orogeny following amalgamation of the North China and Angara cratons. Latest magmatism is marked by the emplacement of the Shangshuiquan monzogranite at 142.2F1.3 Ma, which is most likely related to an underplating event that took place in the Dongping and its adjacent areas at ca. 140 Ma. More importantly, these results suggest that gold mineralization in the area, essentially a single event as indicated by similar deposit characteristics, is broadly coeval with this latest granite magmatism. Hence, this mineralization is about 250 Ma later than the emplacement of the Shuiquangou alkaline complex and, thus, is interpreted to preclude the widely accepted model that suggests gold deposits have genetic relationships with alkaline magmatism. The late timing of gold mineralization with respect to felsic magmatism in the area is similar to those observed in other major gold-producing provinces in the NCC. In all these major gold provinces, we suggest that gold mineralization is coeval with the latest granite magmatic event at about 140–120 Ma. This farther suggests that these mesothermal gold deposits were formed from similar tectono-magmatic environments
    SHRIMP U-Pb zircon Ages of Granitoids in the Wulasha Gold Deposit,Inner Mongolia,ChinaTiming of Mineralization and Tectonic Implications [查看] LAICHENGMIAO、YUMINQIU、NEALMCNAUCHTON、WEIMINGFAN、DAVIDI.GROVES、MINCUOZHAI
    Abstract:The wulashan gold deposit,situated along the northwestern margin of the North China Craton(NCC),is hosted by ductile-brittle faults with Archean metamophic volcano-sedimentary rocks of the Wulashan Group.This deposit is characterized by gold-bearing quartz-K feldspar and quartz veins.Both granitoid batholiths and pegmatite dikes intruded the metamorphic basement rocks,and are spatially associated with gold mineralization.Contrasting genetic medels have been proposed for the deposit due to lack of reliable age data.Our new SHRIMP U-Pb zircon ages for these intrusions now reveal important constraints on the mineraliztion time and tectonic evolution of this region.These intrusions contain inherited zircons of about 2.55Ga.probably from the Wulashan basement that was intruded by pegmatite dikes at about 1.84Ga:the latter probably are related to the major tectonic event leading to the final amalgamation for the NCC.The basement subsequently underwant at least three tectono-thermal events during Phanerozoic time(at353±7，169±7，and 132±2Ma）。 Combined with previous Ar-Ar and K-Ar ages,we suggest two gold mineralization episodes for the Wulashan gold deposit.The first episode occurred at about 350Ma .incicated by ages of a gold-related fuchsite and the Dahuabei granitoid batholith.This supports a previously proposed medel the relates gold mineralization to the Dahuabei granite the formed during collision of the Paleo-Mongolian block with the NCC.The second one occurred in the late Yanshannian period.as indicated by the mineralized K-feldspar-rich vein of 132±2Ma.This episode is simultaneous with those in the eastern NCC.indicative of a widespread late Yanshannian metallogenic event that was a response either to the subduction of lzanagi-Pacific plate beneath eastern China or to the removal of the Early Cretaceous lithosphere in the eastern NCC.
    Petrogenesis of late Triassic post-collisional basaltic rocks of the Lancangjiang tectonic zone, southwest China, and tectonic implications for the evolution of the eastern Paleotethys Geochronological and geochemical [查看] YuejunWang、AimeiZhang、WeimingFan、ToupingPeng、FeifeiZhang、YanhuaZhang、XiawuBi
    The Xiaodingxi and Manghuihe volcanic sequences represent key components of the Lancangjiang igneous zone in southwest China. Their petrogenesis provides important constraints on the tectonic evolution of the eastern Paleotethys ocean. The basaltic rocks from the Xiaodingxi and Manghuihe sequences yield SHRIMP zircon U–Pb weighted mean ages of 214±7 Ma and 210±22 Ma, respectively, which is 15–20 Ma younger than the ages of the syn-collisional granite magmatism (230–241 Ma). Samples from the volcanic sequences are dominated by alkaline basalts and basaltic andesites, and can be geochemically classified into two groups. Group 1 samples, mainly from the Xiaodingxi sequence and the lower part of the Manghuihe sequence, are characterized by low MgO(1.49–7.50 wt.%) and Zr/Nb (9.4–15.3), and high Al2O3 (15.95–18.39 wt.%). They are enriched in LILE and LREE contents and depleted in HFSE, and have 87Sr/86Sr(t) ratios of 0.705473–0.706972,εNd(t) of −1.47–0.75, and similar Pb isotopic compositions to the global average composition of pelagic sediments. In contrast, Group 2 samples from the middle–upper parts of the Manghuihe sequence have similar Al2O3 (16.62–18.23 wt.%) but higher MgO (8.08–11.74 wt.%) and Zr/Nb (15.9–23.9) than those of Group 1 samples. They exhibit relatively flat REE patterns, significantly negative Nb–Ta and Th–U anomalies and positive Sr anomalies. In comparison with Group 1, Group 2 samples show higher Cr, Ni contents and εNd(t) values (1.17–5.02), and lower 87Sr/86Sr(t) and Pb isotopic ratios (Δ8/4=43.2–59.8 andΔ7/4=11.8–19.8). The geochemical data suggest that Group 1 samples might be the differentiated product of primitive high MgO and low Al2O3 melts originating from a refractory modified mantle with the involvement of 5–10% recycled pelagic sediments. The parental magma for Group 2 samples may have been derived from a plagioclase-rich,garnet-free source comprising 80–85% fluid-metasomatized and 15–20% asthenospheric components. Based on all available data, a tectonic model involving eastward subduction in the Permian and collision in the Triassic can be proposed for the evolution of the eastern Paleotethys ocean. During the late Triassic, the progressive upwelling of the asthenospheric mantle, shortly after slab detachment, may have led to the melting of the metasomatized mantle wedge, resulting in the post-collisional Group 1 and Group 2 magmas.
    Mesozoic Multi-phase Magmatism and Gold Mineralization in the Early Precambrian North China Craton, Eastern Hebei Province, China SHRIMP Zircon U-Pb Evidence [查看] LAICEHNGMIAO、YUNMIANQIU、WEIMINGFAN、FUQINZHANG
    The early Precambrian North China craton(NCC) in eastern Hebei Province(also known as the Jidong area) was intruded by granitic batholiths and plutons spatially associated with gold deposits.No consensus has been reached regarding timing and tectonic setting of the gold deposits,chiefly due to the lack of reliable geochronological data.The gold deposits in the district are localized by NE-striking faults within granite plutons and/or nearby Archean amphibolites,as well as in Proterozoic sedimentary rocks.Gold mineralizations in the area are characterized by quartz(±albite)vein-and sulfide-disseminated styles:both types of ores have relatively low sulfide contents(＜10 vol%) and similar sulfide mineral assemblages dominated by pyrite+chalcopryrite+pyrrhotite+galena+sphalerite.locally with molybdenite,tellurides,and bismuthinoids.The alterations around the gold lodes include K-feldspathization,sericitization,silicification,chloritization,and sulfidation,Previous fluid inclusion data from all the deposits of the district show that the mineralizing fluids are characterized by relatively high salinities(3 to 17wt% NaCl equiv.)H2O-CO2±CH4，N2 solutions,with CO2 contents in the inclusions ranging from 5 to 40 mol%.Fluid inclusion homogenization temperatures are between 240 and 400℃,and estimates of the trapping presures vary significantly from 0.5 to 3.7Kba.Stable isotope(O,H,S,C,and Pb)data from these deposits indicate a major magmatic component in the mineralizing fluids and the ore-forming materials,with a partial contribution by Archean host rocks,suggesting that these deposits are basically intrusion-related. SHRIMP zircon U-Pb geochronology of the gold-hosting granitic intrusions,in combination with previous Ar-Ar and Rb-Sr dates on hydrothermal minerals)e.g.sericite),indicates that there was no Archean gold mineralization,but instead suggests that at least three episodes of granitic magmatism and associated gold mineralization took place druing the Mesozoic,The first episode occurred in the Late Triassic at ~222Ma,with emplacement of the Dushan granite batholith(223±2Ma).Aanjia granite porphyry(222±4Ma),and the Baizhangzi granite(222±3Ma）.This episode of magmatism and gold mineralization was coeval with collision of the NCC with the South Mongolian block in the north along the Solonker suture and with the Yangtze craton in the south along the Dabie-Sulu suture.The second episode took place in the Early Jurassic,with emplacement of the Qingshankou granite(199±2)Ma,and the third episode occurred in the Middle Jurassic,with intrusion of the Yuerya(~175Ma)and Niuxinshan(172±2）Ma and granites. These two events are about 25 and 45 Ma later than the coliision of the NCC with other continental blocks in a post-collisional environment.
    Mesozoic Multi-phase Magmatism and Gold Mineralization in the Early Precambrian North China Craton, Eastern Hebei Province, China SHRIMP Zircon U-Pb Evidence [查看] LAICHENGMIAO、YUMINQIU、WEIMINGFAN、ANDFUQINZHANG
    The early Precambrian North China craton (NCC) in eastern Hebei Province (also known as the Jidong area) was intruded by granitic batholiths and plutons spatially associated with gold deposits. No consensus has been reached regarding timing and tectonic setting of the gold deposits, chiefly due to the lack of reliable geochronological data. The gold deposits in the district are localized by NE-striking faults within granite plutons and/or nearby Archean amphibolites, as well as in Proterozoic sedimentary rocks. Gold mineralizations in the area are characterized by quartz (± albite) veinand sulfide-disseminated styles; both types of ores have relatively low sulfide contents (<10 vol%) and similar sulfide mineral assemblages dominated by pyrite + chalcopyrite + pyrrhotite + galena + sphalerite, locally with molybdenite, tellurides, and bismuthinoids. The alterations around the gold lodes include K-feldspathization, sericitization, silicification, chloritization, and sulfidation. Previous fluid inclusion data from all the deposits of the district show that the mineralizing fluids are characterized by relatively high salinities (3 to 17 wt% NaCl equiv.), H2O-CO2 ± CH4, N2 solutions, with CO2 contents in the inclusions ranging from 5 to 40 mol%. Fluid inclusion homogenization temperatures are between 240 and 400°C, and estimates of the trapping pressures vary significantly from 0.5 to 3.7 kbar. Stable isotope (O, H, S, C, and Pb) data from these deposits indicate a major magmatic component in the mineralizing fluids and the ore-forming materials, with a partial contribution by Archean host rocks, suggesting that these deposits are basically intrusion-related. SHRIMP zircon U-Pb geochronology of the gold-hosting granitic intrusions, in combination with previous Ar-Ar and Rb-Sr dates on hydrothermal minerals (e.g., sericite), indicates that there was no Archean gold mineralization, but instead suggests that at least three episodes of granitic magmatism and associated gold mineralization took place during the Mesozoic. The first episode occurred in the Late Triassic at ~222 Ma, with emplacement of the Dushan granite batholith (223 ± 2 Ma), Sanjia granite porphyry (222 ± 4 Ma), and the Baizhangzi granite (222 ± 3 Ma). This episode of magmatism and gold mineralization was coeval with collision of the NCC with the South Mongolian block in the north along the Solonker suture and with the Yangtze craton in the south along the Dabie-Sulu suture. The second episode took place in the Early Jurassic, with emplacement of the Qingshankou granite (199 ± 2 Ma), and the third episode occurred in the Middle Jurassic, with intrusion of the Yuerya (~ 175 Ma) and Niuxinshan (172 ± 2 Ma) and granites. These two events are about 25 and 45 Ma later than the collision of the NCC with other continental blocks in a post-collisional environment.
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