Mineralogical Study Of The Zhuxi Giant Skarn Tungsten Deposit And Its Genetic Implications,Jiangxi Province,China

The Jiangxi Zhuxi tungsten deposit is a newly discovered super-large tungsten deposit.It is located in the eastern part of the Jiangnan orogenic belt.The proven tungsten reserves in the Zhuxi mining area have reached 3.44 million tons,which is the world's largest tungsten deposit.The discovery of Zhuxi world-class super-large tungsten deposit is of great significance for the development of tungsten resources and the research of tungsten deposits.Based on a summary of previous studies,this study has conducted various analysis of garnet and scheelite in the Zhuxi tungsten deposit by in situ methods,using EPM and LA-ICP-MS.The age of the Zhuxi tungsten mineralization was analyzed.The ore bodies of the Zhuxi tungsten deposit are mainly located in the skarn zones between felsic intrusive rocks of Yanshan period and carbonate strata.According to the association and metasomatism relationship of minerals,the mineralization stages were divided into three stages: the early skarn stage,the late skarn stage,the quartz-sulfide stage and the calcite stage.Garnet in Zhuxi tungsten deposit can be divided into two generations: Grt1 and Grt2.According to the electron microprobe analysis,garnet is mainly composed of grossularite-andradite.Grt1 presents more oscillatory zonation texture.LA-ICP-MS was used to analyze trace elements in garnet.The garnet samples are strongly depleted in large ion lithophile elements,including Rb,Ba and Sr and enriched in high field strength elements,such as U and Nd.The total amounts of rare earth elements in garnet samples are low,and the variation range is small,? REE =1.91-21.65 ppm.In comparison,the total amounts of rare earth elements and the ratios of LREE / HREE of Grt2 are generally higher than Grt1,and the U contents of the two garnet generations are quite different.The contents and variation characteristics of major and trace elements in garnets indicate that the fluids in the early skarn stage belong to a relatively open system with a high oxygen fugacity,and infiltration metasomatism is dominated in this system,mainly resulting in garnets with oscillatingzones(Grt1).In the late skarn stage,the fluid evolves into a relatively closed system with a relatively low oxygen fugacity,where the diffusion metasomatism dominates and forms the garnets without zones(Grt2).Based on occurrences and petrographic relationships,scheelite in the Zhuxi tungsten deposit can be divided into four types: one occurs as disseminations in greisen or greisenization marble,the second is disseminated in the early skarn altered ores,the third is disseminated in the late skarn altered ores,and the last occurs in the quartz-sulfide veins crosscutting the skarn altered ores.The electronic microprobe data show that the main elements of scheelite are simple,and the trace and rare earth elements of scheelite are distinctly different for the different types of scheelite.In general,the light rare earth elements are enriched and the heavy rare earth elements are depleted.According to the REE distribution characteristics of scheelite,it indicates that the ore-forming fluid has undergone a transition from oxidizing environment to reducing environment.The in-situ LA-ICP-MS U-Pb dating of garnet in the Zhuxi tungsten deposit shows that the mineralization age of the Zhuxi tungsten deposit is 147.63±3.59 Ma,which belongs to the Yanshanian period.The obtained age is similar to previous ages,indicating that the Zhuxi tungsten mineralizatin is closely related to the magmatic activity in the Yanshanian period in southern China.