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    Devonian A-type granitic magmatism on the northern margin of the North China craton,SHRIMP U-Pb dating and Hf isotopes of the Hongshan granite at chifeng,inner mongolia,China [查看] YuruoShi、DunyiLiu、LaichengMiao、FuqinZhang、PingJian、WeiZhang、KejunHou、JunyuXu
    We report first data for the Devonian Hongshan A-type granite along the northern margin of the Precambrian North China Craton. The granite is rich in silica (SiO2=76.07–77.62 wt.%) and alkalis (Na2O+K2O=8.45–8.78 wt.%), but poor in calcium (CaO=0.28–0.70 wt.%) and magnesium (MgO=0.08–0.20 wt.%). Chondritenormalized REE patterns for the samples fromtheHongshan granite show significant negative Eu anomalies (Eu/Eu*=0.13–0.19). They contain high Rb, Ga, Y, Nb, and Zn, but low Ba and Sr contents, and in the multi-element spider diagrams normalized to primitive mantle, they show a similar pattern to that of A-type granites, such as negative Ba, Nb, Ta, Sr, P and Ti anomalies. Geochemical plots also show an affinity with A-type granites and suggest a post-orogenic setting (A2 type granite). SHRIMP U–Pb zircon dating yielded a concordant weighted mean 206Pb/238Uage of 387±4 Ma,which defines a Devonianmagmatic event. The zircons have negative εHf(t)of −8.4 to−11.5 and give old Hf model ages of TDM2=2548–2820 Ma (mean 2667Ma). Most 176Hf/177Hf and εHf values display Hf-isotope evolutional line of the lower continental crust. These results suggest that the Hongshan granite originated from melting of Archaean lower crust beneath the North China Craton in a post-orogenic extensional setting during the Devonian.
    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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