| The Anle Sn-Cu-Pb-Zn-Ag deposit,is located in the southern part of the Huanggang-Ganzhuermiao metallogenic belt in the southern Da Hinggan Mountains,it is a medium-sized deposit dominated by Sn-Cu with associated Pb-Zn-Ag.Orebodies of the deposit are hosted in faulted and shattered zones,which develop within the Linxi Formation of Upper Permian sandstone and slate.However,the genetic mechanism of the deposit is unclear,In this paper,zircon and cassiterite LA-ICP-MS U-Pb dating,geochemistry,sulfide in-situ S-Pb isotope and trace elements are carried out to provide constraints on petrogenesis,metallogenic mechanism and geodynamic background.The major obtained achievements in this thesis are following:1.The mineralization of the deposit can be divided into four stages,namely,quartz-chlorite-cassiterite-arsenopyrite stage(stage I),quartz-chlorite-cassiterite-arsenopyrite-pyrite stage(stage II),quartz-chlorite-galena-sphalerite-silver-bearing mineral stage(stage ?).2.Geochemically,granite pophyry has high concentrations of SiO2(75.76%?76.67%)FeOT/MgO(18.4?20.8),10000×Ga/Al(3.36?4.61),zircon saturation temperature(808.69?815.52?)and low contents of MgO(0.06%?0.07%),TiO2(0.05%?0.06%)and P2O5(0.01%),with tetrad effect(TE1,3>1.1)of rare earth elements and distinctly negative?Eu(0.01?0.02)anomalies.The rock is characterized by high contens of Rb,U,Ta,Nd and Hf,and low contents of Ba,K,Sr,P and Ti.These features indicate that the Anle granite pophyry belongs to highly evolved A-type granite.The Anle granite pophyry with Sn content(12.7?23.7×10-6;average=17.6×10-6)contributed most of the ore-forming materials,while the highly fractionated and low magma fO2(Ce4+/Ce3+range from5.09 to 84.34)nature of the Anle granite pophyry would have facilitated development of Sn mineralization.3.The?34Sv-CDT values of metallic sulfides in situ LA-ICP-MS range from-4.56 to-3.11‰,and the 206Pb/204Pb,207Pb/204Pb,and 208Pb/204Pb values of metallic sulfides in situ LA-ICP-MS vary from 18.230 to 18.348,15.520 to 15.661 and 38.022 to 38.497,respectively,indicating that the ore-forming material of the deposit chiefly originated from the granitic magma.Co/Ni>1 in in-situ LA-ICP-MS trace elements of pyrite indicates that pyrite was formed in hydrothermal fluid.The results show that the studied chalcopyrite is enriched in Zn,Ag,In and Sn,and is depleted in Co,Ni,Ga,Ge,As,Cd,Sb,Bi and Pb.The high Sn contents(211?2481?g/g) and moderate Cd/Zn ratio(0.0029?0.0071)of the chalcopyrite imply that the hydrothermal Cu mineralization in the Anle deposit was influenced by reduced,high temperature,magmatic-hydrothermal fluids.4.LA-ICP-MS cassiterite U-Pb age is 146.4±2.7 Ma,indicating that the Anle tin-polymetallic deposit formed in the Early Cretaceous.LA-ICP-MS zircon U-Pb dating results show that the Anle granite porphyry,Anle cryptoexplosive breccia,Mopanshan syenogranite and Zhuanshanzi granodiorite in the Anle area were formed at 144.0±2.6 Ma(MSWD=3.2),143.0±1.6 Ma(MSWD=0.7),141.6±1.0 Ma(MSWD=0.41),249.9±1.9 Ma(MSWD=1.9),respectively,implying that the Anle deposit has a close genetic link with the Anle granite porphyry.5.The S-Pb isotopic compositions of the Anle Sn-polymetallic deposit are similar to those of the magma-derived polymetallic deposits in the southern Da Hinggan Mountains,indicating its close relationship with the Early Cretaceous highly differentiated and low-oxygen fugacity granite porphyry,i.e.,it is the product of the gradual evolution of deep magmatic fluid.Inferred from the fact that the Late Yanshanian granite porphyry is closely related to regional mineralization,this study preliminarily believed that the Sn-polymetallic deposit in the Anle deposit is controlled by the acid intrusion-subvolcanic rocks and faults formed by lithospheric extensional setting caused by subduction and retreat of the paleo-Pacific plate and upwelling of asthenosphere in early Cretaceous,which demonstrate that it is a middle-high temperature hydrothermal Sn polymetallic deposits. |
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