Characteristics And Evolution Of Ore-forming Fluids And Mineralization Model For The Weilasituo Tin Polymetallic Deposit,Inner Mongolia

The Weilasituo tin polymetallic deposit is located in south Great Xing'an Range Non-ferrous metallogenic belt.The ore-forming process is closely related to the alkali feldspar granite at depth.By means of petrography,micro-thermometry,and laser Raman spectroscopy analysis,this paper studies on the characteristics of fluid inclusions in the various phases of the Weilasituo deposit from time and space dimensions,such as ore-forming rock mass alkali feldspar granite,greisen,cassiterite sphalerite quartz veins and the chalcopyrite sphalerite ore.Then established the metallogenic model of the Weilasituo deposit preliminarily.The following results have been achieved:1)The metallogenic stage of the Weilasituo tin polymetallic deposit is redefined.The mineralization is divided into four stages:The magmatic stage,greisenization stage,cassiterite sphalerite quartz stage,and sulfide stage.2)From alkali feldspar granite to greisen,cassiterite sphalerite quartz veins and the chalcopyrite sphalerite ore,the fluid inclusions from Weilasituo tin polymetallic deposit varies evidently,from melt inclusion to melt-fluid inclusion and fluid inclusion.The homogenization temperature and salinity of the fluid inclusion decrease from greisen to cassiterite-sphalerite quartz veins The homogenization temperature of the vapor-liquid phase of the melt-fluid inclusion in greisen is similar to that of the fluid inclusions,and the solid phase composition is consistent with the composition of the melt-fluid inclusion.The ore-forming fluid evolution process is continuous from magmatic state through magma-hydrothermal transitional state and to hydrothermal state.3)The laser Raman spectroscopy analysis suggests that the solid phase in melt inclusion contains mainly albite,with minor muscovite and fluorite,while in melt-fluid inclusion only topaz is observed.Magma-hydrothermal transitional fluid,the end stage of magmatic evolution of Weilasituo,is enriched with F.The presence of volatile substances such as F and H₂O can greatly reduce the crystallization temperature of the melts,affecting the mineral composition and crystallization sequence.The granitic magma of saturated F is prone to liquid immiscibility,which is beneficial to the differentiation and evolution of magma.Thus,W,Sn and other metallogenic elements are enriched in late melt and hot water.So the appearance of topaz may indicate the beginning of tin mineralization.4)From the two angles of time and space,the metallogenic model of the Weilasituo tin deposit has been established preliminarily.The tin mineralization has begun in the end stage of magmatic evolution,and the mineralization is the strongest in the hydrothermal phase.The whole process is the result of the complete evolution of the magma in the same period.The mineralization is continuous from the magmatic stage to magma-hydrothermal transitional fluid stage and hydrothermal stage.