The Metallogenic Model And Evolution Of Structural-fluid Study Of Baigan Lake W-Sn Deposit,Ruoqiang, Xin Jiang Province

Baigan Lake tungsten-tin ore field,located in Xinjiang province, contains four deposits,Kekekaerde,Baigan Lake deposit, Bashierxi and the Awar.All deposits mineralization show similar geology character as multiple type in single deposit area and related to stratigraphy, structure and magmatism.We can defined structure as pre-ore-forming stage, ore-forming stage and post-ore-forming stage,the later of which always inherit,replace,superpose the former stucture.Ore-forimg stage took place in Caledonian. Different scale level can also be recognized as regional scale,ore-field scale and orebody scale. Regional scale Baigan lake fault play a role as controlling the distribution of stratum and intrusions,both are close with mineralization. The Secondary faults of Baigan lake fault and intrusive contact structure zone control Ore-hosting structure,including parallel and echelon shape.Fluid inclusions in the three stage quartz can be divided into five types:G-L two phases, G-L-D three phases,CO2or water single phase,CO2-H2O three phases,and CO2-H2O-NaCl four phases. The first two are the main types in stage one quartz. Ore-forming satge quartz vein can be divided in two period and the first period was major W-Sn precipitating period and have all the five types of fluid inclusion.post-mineralization quartz contains mainly G-L two phases type. Ramman analysis results show that the liquid composition contains H2O and CO2while the gaseous composition contains minor CH4and N2as well. H-O isotopic composition of fluid inclusions in the three type veins indicate that ore-forming fluid is a mixture of magmatic water,atmospheric water and metamorphic water.Study on petrographic, microthermometry,and H-O isotopic analysis impy fluid immiscibility and fluid mixing, which may play a significant role for tungsten precipitation.Composite body intrusive this deposit area.Moyite and adamellite emplaced in north-eastern area show as composite body which have similar contemporary and geochemical characteristic.Zircon U-Pb age obtained by SIMS technique are422±3Ma and421±4Ma respectively,indicating mid-late Silurian.40Ar/39Ar plateau age of muscovite from ore-forming alternative granite dike is411.7±2.6Ma while age muscovite from W-Sn quartz vein is412.8±2.4Ma,indicating that Magmatism and mineralization events is continuous.Composite pluton has the characteristics of the A-type granites,diagenetic background stretch stress field of late orogenic environment. Pluton which is rich in ore-forming elements is not noly the parent rock of Baigan Lake tungsten-tin-polymetallic mineralization, but also white Baigan tungsten polymetallic ore field intothe center of the mine system.Metallogenic model can be described as sedimentary-metamorphic deformed mineralized period-agmatism hydrothermal mineralization period-supergenesis period. Magmatism hydrothermal ore-forming period was futher divided into veinlets formative stage, stratiform tungsten-tin ore body formation stage and W-Sn quartz vein ore body formation stage.