A Study On The Metallogenic Mechanism Of The Caledonian Niutangjie Tungsten Deposit In The Northern Guangxi,Western Nanling,China

Many multi-aged tungsten polymetallic deposits or occurrences occurred in Miaoershan-Yuechengling batholith,Northern Guangxi.Niutangjie stratabound skarn-type tungsten deposit located in the southwest of Yuechengling batholith,is the largest and most typical tungsten deposit in this area.The ore bodies in this tungsten deposit are large and the slightly chloritized granites closely associated with ore bodies are medium-fine grained muscvite granite.The whole rock chemical analyses indicate that Niutangjie granites are peraluminous and concentrate tungsten,which belong to highly fractionated parental granites and were formed by the partial melting of the crustal basements.Zircon U-Pb dating of the parental granite yielded a diagenetic age of 410± 4.9Ma and the situ U-Pb dating of apatites co-existed with scheelites yielded a metallogenic age of 418 ± 37Ma,the two ages show that the diagenesis and mineralization of Niutangjie tungsten deposit belong to Caledonian.The mineralization of Niutangjie tungsten deposit was strong and formed many different types of ores.This paper carried out a systematic study on the ores of Niutangjie tungsten deposit,according to the alteration type,three different and most importan types of ores were divided:skarn-type ore,chloritized ore and quartz vein(lump)-type ore.According to the mineral assemblages and mineral forming sequences,the formation of the three different types of ores can be corresponding to different mineralization stages:skarnization satge,quartz-sulfide stage and the late silication-carbonation stage.Through the in situ trace elements analyses of scheelites,this paper reveals the mechanisms how REE were substituted into scheelites formed in each mineralization stage and elucidates Combined the characteristics of REE distribution curves with petrographic.It also elucidates the evolution process of metallogenic fluid and the variation of the oxygen fugacity in the metallogenetic environment from early skarnization stage to late silication-carbonation stage.In addition,this paper also carried out the oxygen isotope analyses of scheelites,combined with the previous oxygen isotope works showing that the metallogenic fluid is magmatic water mixed with atmospheric water and the highly fractionated parental granite is an important source of metallogenic materials.In this deposit the pores in the second member of Cambrian Qingxi formation((?)q2)are well developed and they are important ore storage spaces.The ore bodies in this tungsten deposit are enclosed by several groups of arc fractures,and the entire Niutangjie tungsten deposit is controlled by the Xin-Zi fault in the east.The formation of Niutangjie tungsten deposit is the result of the favorable magmatic,stratigraphic and tectonic interaction in this area.