Late-Mesozoic Silver-Lead-Zinc Metallogenetic System In The Middle Section Of Erlian-East Ujimqin Banner Metallogenetic Belt

The middle section of Erlian – East Ujimqin Banner Metallogenetic Belt is located at the eastern section of the China-Mongolia border, inside of China. A cluster vein-type Ag-Pb-Zn deposits and occurrences were discovered in recent years, of which metallogenetic type are low to moderate temperature hydrothermal fracture filling deposits. Three typical deposits, Ganzhuershande, Hadate Tolgoi and Gaoerqi, have similar ore geological characteristics. The occurrence of mineralization zone and orebodies are strictly controlled by tensional fractures. All of the three deposits have similar ore texture, structure, and the signatures of mineralization. Quartz- sericite- pyrite alteration is the predominant wall-rock alteration. The whole mineralization process can be subdivided into three stages: early, main and late stage. Early stage is characterized by quartz-sericite-pyrite; main stage forms abundant quartz and sulphide; and the late stage is exhibited by quartz-carbonate-fluorite.The research result of geochemistry and geochronology of granites indicates that the Ganzhuershande pluton, as a typical example of late-Carbaniferous I-type granite, yield a dating result of 298±1Ma ~ 301±1Ma by zircon LA-ICP-MS U-Pb method. The tectonic settings discriminant diagrams of major elements and trace elements indicate that the Ganzhuershande pluton belongs to post-collision granite in the late stage of orogeny, which is inferred as the product of magmatic activity during the late stage of collision between Siberia plate and North China plate along Eranhot-East Ujimqin Banner. The late-Carbaniferous granitoid has no relationship with Ag-Pb-Zn mineralization. The late-Mesozoic A-type granite, represented by Hadate Tolgoi pluton, is dated at the age of 125.6±4.3Ma by the method of zircon LA-ICP-MS U-Pb, forming in the extensional tectonic settings in the continental margin, is concluded to be generated in the post-orogeny extensional stage after the closure of Mongol-Okhotsk Ocean. The late-Mesozoic granitoid is closely associated with the Ag-Pb-Zn mineralization.Sulfur isotope and lead isotope suggest that the Ag-Pb-Zn deposits have identical source of ore-forming sulfur materials related to granitic magmatism, of which the lead originated from the mixture of upper crust and mantle. 40Ar/39 Ar dating of altered sericite samples from Ganzhuershande deposit demonstrating the Au-Pb-Zn mineralization of Ganzhuershande deposit occurred around 144.3Ma ~ 145.9Ma. According to the geochronology results of Late-Mesozoic granite associated with mineralization in the region, it is concluded that a series of Ag-Pb-Zn deposits and occurrences formed during the consecutive alkaline magmatism and metallogenesis in Late-Mesozoic 145.9Ma ~ 125.6Ma, of which the tectonic settings is post-orogeny extensional continental margin after the collision between Mongol-North China united plate and Siberia craton along the Mongol-Okhotsk suture zone. Through summarizing controlling factors for metallogeny, metallogenic process and post-ore modification and preservation of mineral deposits, the Late Mesozoic Erlian- East Ujimqin Banner Ag-Pb-Zn metallogenetic system was established.Based on the comparison of ore-controlling structures, soil geochemistry and geophysics characteristics of Ganzhuershande, Hadate Tolgoi and Gaoerqi deposits, the exploration targets for Ag-Pb-Zn deposits in the middle section of Erlian – East Ujimqin Banner metallogenetic belt are summarized as below: identifying the prolongation and extension according to the attitude and en-echelon array of tensional fractures; and designing exploration engineering aiming to the overlapped area by geochemical anomalies, chargeability high, and sericite alteration.