| The Wunur Zn-Pb-Ag-Mo polymetallic deposit is a newly explored ore deposit in Wunur Town,Yakeshi City,Inner Mongolia,NE-China.It is of great significance to reveal the metallogenic mechanism and establish the metallogenic model of the Wunuer deposit for futher mineral Exploration in this area.Formation of the Wunuer deposit is closely related to the Late Jurassic-Early Cretaceous volcanic-subvolcanic rocks in deposit area,and the deposit shows features of both porphyry-type mineralization and epithermal-type mineralization.The metallogenic process of the Wunuer deposit can be divided into two metallogenic periods,and can be subdivided into three metallogenic stages:(1)Quatz vein-type Mo mineralization stage,mainly occurred in the apical portions of the granite porphyry intrusion in deep position,had formed molybdenum ores principally composed of molybdenite vein and molybdenite-quartz vein.The associated magmatic rock had commonly suffered typical porphyry type alteration such as potassium,silicification,chloritization,pyritization and beresitization alterations;(2)Cryptoexplosive breccia-type Zn mineralization stage,mainly occurred in the cryptoexplosion breccia hosted by granite porphyry and Manketouebo Formation volcanic rocks adjacent to the intrusion in intermediate position,had formed zinc ores principally composed of sphalerite-pyrite cemented breccias.The associated host rocks had commonly suffered chloritization and sericitization alterations;(3)Epithermal-type Zn-Pb-Ag mineralization stage,mainly occurred in the Manketouebo Formation volcanic rocks in shallow position,had formed brecciated,veined and stockwork Zn-Pb-Ag ores principally composed of sphalerite,galena,and chalcopyrite.The associated wall rocks had commonly suffered pyritization,kaolinization and pyrophyllitiazation alterations.The ore-bearing wall rocks of Manketouebo Formation(rhyolite:144.9±0.57 Ma;tuff:145.6±2.2 Ma)and the ore-forming related granite porphyry intrusion(144.5±0.6Ma)have near zircon U-Pb ages,which are similar to the ore deposit metallogenic age(143.8±0.6 Ma),indicating that the Wunur deposit is a typical volcanic-subvolcanic hydrothermal deposit.The Manketouebo Formation volcanic rocks and the granite porphyry have similar geochemical characteristics,with higher contents of SiO2,Al2O3and lower contents of CaO,MgO,TiO2,TFe2O3 in major elements.The trace elements are characterized by enrichment of Rb,Th,U,Zr,Hf,and depletion of Ba,Sr,P,Ti,Ta and Nb,and are characterized by strong enrichment in LREEs,flat HREEs distribution pattern and marked negative Eu anomalies.Whole-rock geochemistry,Hf isotope and Pb isotope characteristics show that the ore-bearing wall rocks and ore-forming related granite porphyry intrusion in the Wunur deposit area are derived from the same magma chamber with a strong fractional crystallization formed in the post-collision extensional structure background,which belongs to alkali-calcic series,highly differentiated A-type granitic cock,formed by the partial melting of the mantle-derived juvenile basaltic lower crust accompanied by minor crustal material.Two generations of sphalerite,with the first-generation sphalerite precipitated in cryptoexplosive breccia-type Zn mineralization stage and the second-generation sphalerite precipitated in epithermal-type Zn-Pb-Ag mineralization stage,were identified in the Wunuer deposit.The first-generation sphalerite is generally euhedral and light in color(yellow to brown in transmitted light),and is free of mineral inclusions and replaced by the second-generation sphalerite as well as sulfides,trace elements like Fe,Cu,In in sphalerite are present as solid solution by substitution into sphalerite crystal lattice;the second-generation sphalerite is generally anhedral,opaque and black in color,and contains abundant chalcopyrite disease,trace elements in sphalerite like Fe,Cu,Pb,Ag are greatly attributed to micro-mineral inclusions.Chlorite alteration in the Wunuer deposit is closely related to the cryptoexplosive breccia-type Zn mineralization,calculation result of chlorite composition thermometer is about 330?,which is in accordance with the fluid inclusion study of the first-generation sphalerite.The magmatic zircon U-Pb age of rhyolite of the Manketouebo Formation is144.9±0.57 Ma,the magmatic zircon U-Pb age of tuff of the Manketouebo Formation is145.6±2.2 Ma,the magmatic zircon U-Pb age of the ore-forming related granite porphyry is 144.5±0.6 Ma,so that the upper limit of the metallogenic age of the Wunuer deposit can be restricted to about 144.5 Ma.The U-Pb age of hydrothermal zircon,which is closely related to the porphyry stage mineralization and alteration,is determined to be143.8±0.6 Ma.Therefore,the Wunuer deposit metallogenic age can be restricted to approximately 143.8?144.5 Ma.There is also a 138.9±0.9 Ma aged granite intrusion in the Wunur mining area,which may provide fluid and heat for the epithermal mineralization,and led to its long duration.The sulfur isotope characteristics of sphalerite,galena,and pyrite(?34SV-CDT:0?6‰,)show that metallic materials of the Wunur deposit is mainly derived from magmatic rocks.Lead isotope characteristics(206Pb/204Pb:18.288?18.326,207Pb/204Pb:15.528?15.568,208Pb/204Pb:38.08?38.204)indicate an orogenic belt mixed lead source.In summary,metallic materials of the Wunur deposit is mainly from magmatic rocks derived from the juvenile basaltic lower crust.Based on fluid inclusion measurement,sphalerite crystal chemistry,chlorite thermometer,mineral assemblage,etc.,we concluded that ore-forming fluid in the quartz vein-type Mo mineralization stage is dominated by magmatic fluid with high temperature,high salinity,high oxygen fugacity,high Logf(S2),and high pH;ore-forming fluid in the cryptoexplosive breccia-type Zn mineralization stage is dominated by magmatic fluid mixed with a small amount of meteoric water,with medium temperature,medium salinity,medium oxygen fugacity,medium Logf(S2),and low pH;ore-forming fluid in the epithermal-type Zn-Pb-Ag mineralization stage is mixed by magmatic fluid and meteoric water,with low temperature,low salinity,low oxygen fugacity,low Logf(S2),and low pH.In addition,exogenous Cu-rich fluids may be mixed into ore-forming fluids in the epithermal stage.The Manketouebo Formation volcanic rock,the concealed rock mass,the crosscut of faults and the comprehensive pedogeochemical anomaly,low magnetic anomaly,high polarization,low resistance anomalies are important ore-controlling factors and prospecting information of the Wunuer mining area,based on which we have delineated a porphyry-type Mo-Zn mineralization prospecting target area and an epithermal Zn-Pb-Ag prospecting target in the Wunuer mining area.According to the geological information of the 207-exploration line section,the altered mineral zoning and geochemical primary halo,we predict the the deep part of the 207-exploration line has the prospect of prospecting quartz wein-type Mo mineralization. |
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