The Studies On High-Intermediate Temperature Sn-Rb-Li-W And Intermediate-Low Temperature Cu-Zn-Ag Metallogenic Ore System At Weilasituo,Inner Mongolia,NE China

This work mainly focuses on large and superlarge Sn polymetallic metallogenic ore system,and selects the newly-discovered Weilasituo Sn-Cu polymetallic deposit as a case study.The Weilasituo ore system is characterized by a feature that altered granite type orebody is located in the deep part,the hydrothermal breccia type orebody on the top of the intrusion,the greisen type veins in and adjacent the intrusion,and the hydrothermal mineralized veins nearby the intrusion.Both mineralization and alteration yield evident feature from the core to the boundary of the quartz porphyry,which show that the mineralization follows Rb-Li-(Sn),Sn-(W-Cu-Zn)and Cu-Zn-Ag,and alteration assemblages are albite-K-feldspar-muscovite,muscovite-quartz-illite,and quartz-calcite-muscovite-illite-epidote-flourite.The Weilasituo ore system can be divided into three paragenetic stages,including Rb-Li-Sn alteration-mineralization stage(I),greisen Sn polymetallic stage(II),and hydrothermal Cu-Zn-Ag stage(III).Both Sn and Cu mineralization in Weilasituo have a close genetic relationship with the local quartz porphyry,which is characterized by high Si and Na,peraluminous,high-K calc-alkaline features.This porphyry can be classified as the I type granite.The Sr-Nd-Hf isotopes indicate that the parent magma for the porphyry is derived from the melting of the lower crust.Zircon LA-ICP-MS U-Pb dating reveals that the porphyry formed at 135.7±0.9 Ma,which suggests that the quartz porphyry formed in an extensional tectonic setting.This is closely related to the Paleo-Pacific oceanic subduction.The measured S isotopes for minerals from distinct ore stages are consistent with a magmatic S source.The Pb isotope compositions for ore minerals indicate the metals from a magma.The D and O isotopes also suggest that the fluid is related to a magmatic source.The melt inclusions hosted in the quartz phenocryst and the altered quartz porphyry recorded the transition process from melt to fluid system.Fluid inclusion studies suggest that the homogenization temperatures for Rb-Li,Sn,and Cu mineralization are 313-383,260-323,and 203-240 °C,respectively.Those results suggest that from early to late ore stages the fluid system is cooling,which is important to trigger Cu and Sn mineralization.The cassiterite LA-MC-ICP-MS U-Pb dating results suggest that Sn mineralization occurs between 136.8±3.8 and 141.4±5.9 Ma.The molybdenite samples from Sn mineralization stage have Re-Os model ages from 134.2±1.4 to 140.7±1.5 Ma.The muscovite samples associated with Sn and Mo mineralization yield Ar-Ar ages from 133.7±1.5 to 140.7±1.0 Ma.The muscovite samples from the Cu mineralization stage have Ar-Ar ages of 133.4±0.5 and 133.42±0.5 Ma.The multiple geochronological methods including U-Pb,Re-Os and Ar-Ar reveal that the magmatic-hydrothermal system for the Weilasituo Sn and Cu mineralization lasts over 7 Ma.This long duration is likely related to multiple magmatic-hydrothermal events.Based on the systematic studies,this work proposes that the local Sn mineralization and its nearby Cu mineralization belong to one metallogenic ore system,which is closely related to the local early Cretaceous felsic magmatism.The identification of SnRb-Li mineralization and its related Cu-Zn-Ag mineralization in this region is helpful for ore exploration.