Mineralization Of Ag-polymetallic Ore Deposits In The Eastern Xiaoshan,Henan Province

The Laoliwan and Zhonghe Ag-Pb-Zn deposits in Henan Province,located in the Huaxiong massif on the southern margin of the North China Craton,are both newly discovered large deposits in the Xiaoshan fault uplift.The discovery of the two deposits as well as numerous Ag-polymetallic ore occurrences means that there are huge Ag-polymetallic ore prospecting potential in the shallow cover area of the eastern Xiaoshan.Systematic mineralogy,fluid inclusion,geochronology,and geochemistry were studied for the two deposits in this paper.Ore bodies of the Laoliwan Ag-Pb-Zn deposit are composed of disseminated,veinlet disseminated,and vein-type ores,and most of the ore bodies are hosted in NW-and NNW-extending faults,which develop in the Early Cretaceous granite porphyry,with a small amount of ore bodies occurring within NW-and NNW-extending faults in the Xiong'er Group.Mineralization process of the Laoliwan deposit can be divided into three stages:(1)sericite+sphalerite+galena+pyrite stage(early stage),(2)barite+sphalerite+galena+silver-bearing minerals±carbonate±quartz stage(middle stage),and(3)sphalerite+galena+silver-bearing minerals stage(late stage).The fluid inclusions(FIs)in quartz phenocrysts of the granite porphyry mainly include daughter mineral-bearing(S type)and liquid-rich(WL type)inclusions,with minor gas-rich(WG type)inclusions,and the fluid of the stage belongs to an H2O-NaCl system with high temperature and great fluctuation of salinity.The FIs in barite related to Ag-Pb-Zn mineralization only consist of WL-type inclusions,and the ore-forming fluid of the middle stage belongs to an H2O-NaCl system with medium temperature and low salinity.The ?18OH2O and 8D values of ore-forming fluids in the middle stage vary from 5.9‰ to 8.4‰ and-89.7‰ to-65.5‰,respectively,indicating that the ore-forming fluids mainly originated from magma.The ?13C value of barite varies from-22.9‰ to-12.5‰,which is consistent with the ?13C value of evolutional granitic magma,implying that the ore-forming fluids mainly originated from magma.The ?34S values of metallic sulfides from ores range from 1.9? to 5.9? with an average of 3.5?,and the 206Pb/204Pb,207Pb/204Pb,and 208Pb/204Pb values of metallic sulfides vary from 17.262 to 17.430,15.444 to 15.501,and 37.774 to 38.050,respectively,indicating that the ore-forming material of the Laoliwan deposit chiefly originated from the granitic magma.LA-ICP-MS zircon U-Pb age of the Laoliwan intrusion related to Ag-Pb-Zn mineralization ranges from 137Ma to 133Ma,indicating that the Laoliwan intrusion formed in the Early Cretaceous.The Laoliwan intrusion mainly composed of granite porphyry belongs to a high-K calk-alkaline I-type granite,and its source region is dominated by the Meso-Neoarchean and Paleoproterozoic crustal material with a small amount of the Paleoarchean and Eoarchean crustal material.The magma mixing between basaltic magma generated by underplating and felsic magma formed by partial melting of the ancient crustal material is the primary mechanism responsible for the Early Cretaceous Laoliwan intrusion.The Zhonghe deposit consists of vein-type Ag-Pb-Zn orebodies in the shallow part and porphyry Mo orebodies in the deep part.These Ag-Pb-Zn orebodies are mainly controlled by NNE-trending faults,followed by near horizontal fracture zones that were formed by condensation and shrinkage of the rock mass.Mineralization process of the Zhonghe Ag-Pb-Zn deposit is preliminarily divided into two stages:(1)sphalerite+galena±silver-bearing minerals,and(2)sphalerite+galena+silver-bearing minerals stage.The ?18OH2O and 5D values of quartz range from 2.8‰ to 4.9‰ and-98.7‰ to-81.3‰,respectively;the ?13C and ?18O values of calcite range from-2.8‰ to-1.3‰ and 6.2‰ to 8.5‰,respectively;indicating that the ore-forming fluid of the Zhonghe deposit is mainly magmatic water.The ?34S value of metal sulfides ranges from 2.9‰ to 6.1‰ with an average of 4.2‰,and the 206Pb/204Pb,207Pb/204Pb,and 208Pb/204Pb values vary from 17.262 to 17.348,15.444 to 15.501,and 37.804 to 38.050,respectively,indicating that the ore-forming material of the Zhonghe deposit chiefly originated from the granitic magma.LA-ICP-MS zircon U-Pb age of the Zhonghe intrusion related to Ag-Pb-Zn mineralization is 135Ma,indicating that the Zhonghe intrusion formed in the Early Cretaceous.The Zhonghe intrusion mainly composed of granite porphyry belongs to a high-K calk-alkaline I-type granite.The magmatic source region of the Zhonghe intrusion is dominated by a Neoarchean crust with a small amount of Mesoarchean crust,and the intrusion is most likely to be formed by a partial melting of the Meso-Neoarchean crust,which formed in a Meso-Neoarchean island are environment.The Ag-polymetallic mineralization in the eastern Xiaoshan is closely related to the Early Cretaceous granite porphyries,and constitutes a porphyry Mo and medium-low temperature hydrothermal vein type Ag-polymetallic metallogenic system.These vein-type Ag-Pb-Zn orebodies discovered at present belong to the shallow mineralization of the porphyry-hydrothermal vein type metallogenic system.