Fluid Inclusion Characteristics And Metallogenetic Process Of The Weilasituo Tin Polymetallic Deposit,Inner Mongolia

The Weilasituo area is a mining area with important economic value and research significance on the west slope of the southern section of the Great Xingan Mountains.From the beginning of the 20 th century to the present,the survey staff has successively discovered large copper-zinc-silver polymetallic deposits,tin-tungsten-zinc polymetallic deposits and greisen-type lithium polymetallic deposits in the area.Through detailed field geological exploration work and indoor test analysis work in the study area,the geological characteristics of ore-bearing strata,ore-bearing structures,ore-forming geological bodies and related deposits are identified.Through the zircon isotope dating of the ore-forming geological bodies,the formation age of the ore-forming rocky quartz diorite is(337.7±1.5)Ma,which is different from the previous experimental data of(310±2)Ma,indicating that the intrusion of rock mass has multiple stages,magmatic activity is active throughout the Carboniferous(354 ~ 295Ma).This quartz diorite should be the product of magma arc activity,and its formation may be related to the subduction of the ancient Asian Ocean.The metallogenic process in the Weilasituo mining area can be divided into two mineralization periods and six metallogenic stages.Tin polymetallic mineralization period: amazonitization stage,greisenization stage and quartz vein type tin-tungsten mineralization stage;Copper-zinc-silver polymetallic ore-forming period: arsenopyrite-pyrite-molybdenite stage,the metallogenic stage of zinc and copper polymetallic sulphides and the metallogenic stage of lead and silver polymetallic sulphides.There are many types of fluid inclusions in the mining area.There is a gradual change in the type of inclusions in each metallogenic stage.The temperature and salinity of the fluids in different mineralization stages are generally decreasing.The fluid evolution of the whole deposit is continuous.The ore process is the result of the evolution of the same fluid.During the metallogenic period of tin polymetallic ore-forming,the ore-forming fluid is medium-high temperature and has a large range of salinity(The homogenization temperature is 201~ 473°C,and the salinity is 2.7~ 50.9 wt%NaCl);the copper-zinc-silver polymetallic mineralization period is a medium-low temperature,low-salt fluid.The homogenization temperature of the fluid inclusions in the copper-zinc-silver mineralization period of the tin-polymetallic ore district is 140-352 °C,and the salinity 1.7~ 9.1 wt%NaCl,which is highly similar to the fluid characteristics of the copper-zinc-silver district(The homogenization temperature is 152~ 335°C,and the salinity is 3.5~ 12.05 wt%NaCl).It is speculated that the ore-forming process of the entire mining area is the evolution of the same fluid.During the metallogenic period of tin polymetallic ore-forming,the composition of ore-forming fluid is mainly magmatic water.During the copper-zinc-silver polymetallic mineralization period,the atmospheric precipitation in the fluid gradually increases,and the fluid becomes a mixed fluid.Fluid boiling and cooling and cooling processes are the main factors leading to mineralization.The Weilasituo tin polymetallic deposit is a magmatic-hydrothermal deposit affected by alkali-feldspar granite,rather than a porphyry tin deposit affected by quartz porphyry as previously thought.