A Study On The Alteration And Fluid Mineralization Of The Honghuaerji Scheelite Deposit,Inner Mongolia

The Honghuaerji scheelite deposit is a hydrothermal quartz vein type scheelite deposit discovered in the Da Hinggan zone in recent years.The scheelite deposit mainly exists in the quartz vein inside the granite body.The predecessors have done a lot of research on its mineralization,and basically determined the mineralization age of the deposit and the geochemical characteristics of the granite,but the research on the alteration effect is relatively lacking.In this article,we conducted an in-depth study of alteration and fluid action by the petrographical study,electron probe analysis,fluid inclusion research and so on.Moreover,the chronological and geochemical of plaque-like monzonitic granite are studied.Through the study of the alteration distribution,it can be seen that the muscovitization of feldspar and quartz fine vein silicification are the two types of alterations most closely related to mineralization.The hydrothermal fluid may promote the alteration of granite.Petrographical study and electron probe analysis showed that muscovite was secondary muscovite.The results of electron probe showed that the content of scheelite is less,only contains a small amount of NaO,MgO,MnO and FeO.The ratio of muscovite to silicon and aluminum is greater than 3?n?Si?:n?Al?>3:1?,which is formed by alteration.The type of muscovite is potassium polysilicon muscovite.The plagioclase is oligoclase except for medium andesine,and its Ab and An values vary widely,ranging from 69.79%to 89.11%,9.84%to 26.74%.The CaO content of biotite is low,and the mainly type of biotite is lepidomelane.It has high oxygen fugacity which is between Ni-NiO and Fe₂O₃-Fe₃O₄.The crystallization temperature is calculated from 550?to 600?.The magma comes from the mixture of crust and mantle,and it has more mantle source composition.The chlorite is mainly prochlorite,Fe-Mg chlorite,and pycnochlorite.The chlorite in the stratum is lack in Al,Mg,rich in Fe,and all belongs to prochlorite.The zircon U-Pb dating shows that the weighted mean age of plaque-like monzonitic granite is 176.3±0.58 Ma,which is slightly later than other granite but only differs 2.3².9 Ma,And the granite geochemistry results show that the main features are basically the same,only have a medium negative Pr anomaly.Comprehensively,the plaque-like monzonitic granite and other ore-bearing granites belongs to the same period.Fluid inclusion studies show that the fluid inclusions in granite have undergone strong post-modification,with a homogenization temperature range of220.7³89.0?,and the average salinity is 5.44%NaCleqv.The homogenization temperature of scheelite inclusions in the ore-forming stage range of 251.9³86.9?.The average salinity is 6.16%NaCleqv.The salinity decreases with the decrease of temperature in each stage.There may be less meteoric water mixed in the process of fluid evolution.The results of Laser Raman show that the inclusions in each stage are mainly H₂O.The mineralization mainly occurs in the magmatic-hydrothermal transitional fluid.The mass transfer of the fluid promotes the alteration and mineralization.During the process of magma evolution,the magma mixing of different components occurs,and the adamellite inclusions has been formed.