The Study On The Metallogenesis Of The Chamuhan W-Mo Deposit,Hexigten Banner,Inner Mongolia

According to our detailed field work and indoor studies,the new advances on the Chamuhan W-Mo deposit have been made as follows:1.The ore bodies occur in the white medium-grained granite,and the underlying red medium-grained granite and red fine-grained granite.Zircon LA-ICP-MS U-Pb dating shows that the emplacement age of white medium-grained granite is 144Ma.The red fine-grained granite cuts the red medium-grained granite,which has a gradual boundary with the white medium-grained granite.It indicates that the white medium-grained granite are the products of the altered red medium-grained granite.According to molybdenite Re-Os isotopic dating,the deposit was formed in 140Ma,4 m.y.younger than the emplacement age of the white medium-grained granite.2.The major elements show that,all of the three kinds of granites are peraluminous,high in silicon,potassium,low in iron and magnesium.The trace elements are characterized by the depletion of Eu,Ba,Sr,P and Ti.They all have theM-type tetrad effects and the related noncharge-and-radius controlled behavior,which means some key element ratios deviate from the normal range.So we think that the three kinds of granites are highly fractionated granites.Comparatively,the red fined-grained granite is the most fractionated,while the red mediumgrained granite takes second place,and the white medium grained granite is least fractionated.According to zircon saturated thermometer,the three types of granites formed lower than 800?,so they should be not A-type granite.Furthermore,as the granites are peraluminuim with very low concentrations of phosphorus,they are defined as the highly fractionated I-type granites.The whole rock Pb isotopes show that the lead isotope ratios for the three kinds of granites display a linear array,indicating their protoliths are same.The zircon Hf isotope features suggest that their protoliths are derived from the juvenile crust.3.The formation of Chamuhan deposit can be divided into seven stages:silicification,greisenization.albitization prior to mineralization,greisenization during mineralization,and tourmaline-quartz alternation,sericitization and chloritization after mineralization.Using the twofeldspar thermometer,the albitization of white medium-grained granite formed at 335?452?,red medium-grained granite at 382?414?,and red fine-grained granite at 3 85?447?.4.Studies on the fluid inclusions of quartz formed at metallogenic stage show that the ore fluids have a feature of high temperature,high salinity,and high oxygen fugacity,and are rich in CO2.The precipitation temperatures of wolframite are 300?450?,and the precipitation temperatures of molybdenite are 200?400?.The main mechanism of mineral precipitation is fluid boiling.The feature of H-O isotopic data indicates that ore fluid mainly came from magmatic fluid,with the mixture of minor meteoric water.The 834S value of molybdenite is 0?1‰,indicating that the ore-forming materials are derived from the deep source.The Pb isotopic data of molybdenite show that the ore-forming materials have the same source with the granites in the ore district.5.On the basis of the studies above,the Chamuhan W-Mo deposit is a magmatichydrothermal deposit,and the W-Mo mineralization has a close relationship with the white medium-grained granite,red medium-grained granite and red fine-grained granite.Finally,the diagenetic-metallogenic model was created.