Magmatic Evolution And Metallogenic Process Of The Weilasituo Tin Polymetallic Deposit In The Southern Great Xing'an Range

China's W-Sn resources are dominant on a global scale.A series of Sn-polymetallic deposits has been found in recent years at depth on the flanks of known volcanic-subvolcanic Cu-Pb-Zn-Ag deposits in the Southern Great Xing'an Range,NE China.The large-size Weilasituo tin-polymetallic deposit is most typical of these types of deposit.Tin-polymetallic orebodies are hosted in the early Paleozoic Xilingol Complex,and their mineralization is closely related to Early Cretaceous quartz porphyry.Geochemical characteristics indicate that the ore-bearing rock mass(quartz porphyry)is of highly differentiated ?-type granite.Based on detailed petrological and EMPA and LA-ICP-MS analyses of different types of zinnwaldite in the study area,it is found that magmatic zinnwaldite from the upper mineralized part of the quartz porphyry is enriched in Nb(100-160 ppm)and Ta(100-150 ppm),while hydrothermal zinnwaldite from the explosive breccia,quartz veins,and surrounding gneiss is unusually rich in Mg(up to 3.4 wt.%MgO)and Sn(up to 200 ppm).The analysis of quartz and sphalerite shows that zinnwaldite not only affects the distribution of elements during hydrothermal migration,but also plays a role in mineralization.On the basis of collecting a large number of sphalerite trace elements from several deposits around the world,we found that the Ga/Ge ratio increases with the increase of S content in MVT deposits,but the Gd/Fe ratio is the opposite;in Skarn and VMS deposits,the Gd/Fe ratio decreases with the increase of S content.Among all deposit types,when S content in sphalerite is below 31,the relationship between Fe/Zn ratio and S content is y=-0.043x+1.414;when S content is higher than 31,the relationship between Fe/Zn ratio and S content is y=0.862 In(x)-2.894.The metallogenic process in the Weilasituo mining area can be divided into five stages:I:porphyry type stage;?:quartz+cassiterite+wolframite+molybdenite stage;?:quartz+cassiterite+polymetallic sulfide stage;?:quartz+fluorite+pegmatite stage;?:carbonation+montmorillonization stage.The homogenization temperature and salinity for each stage are 282-444 C and 282-444 wt%NaCl eqv,242-346 wt%NaCl eqv,242-346 C and 2.2-344 C,183-344 eqv-8.6 wt%NaCl eqv.Raman results show that CH4 exists in inclusions of all stages and F ions exist in inclusions of stage ?,indicating that the ore-forming fluid is partial reductive and rich in volatile matter.The results of H-O isotopes show that the ore-forming fluids mainly come from magmatic fluids and are influenced by meteoric precipitation in the later stage.3He/4He ratios of the Weilasituo tin-polymetallic and Cu-Zn deposits are in the ranges 3.38-4.91 Ra and 4.8-4.9 Ra,respectively,indicating ore-forming fluids sourced from mixed crustal and mantle materials.Molybdenite Re-Os dating of W mineralization yielded an isochron age of 129.0±4.6 Ma,similar to the porphyry crystallization and mineralization ages of the Weilasituo tin-polymetallic deposit,and also consistent with the mineralization age of the Cu-Zn deposit.We propose a new metallogenic model,with all subtypes of W-Sn-Cu-Pb-Zn-Ag mineralization in the Weilasituo area belonging to a single complex metallogenic system.Compared with other ore districts,ore-related granitoids in the Southern Great Xing'an Range display relatively uniform emplacement ages and were derived from partial melting of juvenile lower crust rather than old basement.Their ore-forming fluid source was influenced by mantle fluids to a higher degree than found in South China.