Mineralogical Characteristics And Its Indication For Mineralization Of Garnet From Zhuxi Supersized Tungsten(Copper) Deposit,Northeast Jiangxi

Zhuxi tungsten deposit in northern Jiangxi Province is located in Fuliang County,Jingdezhen City,Jiangxi Province.It is located at the border between the Yangtze plate and the South China fold belt.It is the largest skarn type tungsten deposit found in the Jiangnan ancient land tungsten ore belt in recent years.How a large amount of tungsten is enriched and mineralized in the process of magmatic hydrothermal evolution is a scientific problem of great concern.Garnet is one of the main minerals formed in the process of skarnization.Its formation records the physicochemical information of skarnization.Based on the mineral assemblage and zoning characteristics of different stages of skarn process,the in-situ micro regional element distribution characteristics of garnet and its associated minerals are systematically analyzed,and the distribution process and physicochemical conditions of tungsten and other metallogenic elements in skarn process are revealed.On the basis of field geological investigation,this paper carried out the geochemical study of major and trace element of garnet.The main understandings are as follows:(1)The mineral symbiotic association characteristics of garnet in Zhuxi tungsten deposit are found out.Garnet in Zhuxi deposit is composed of calcium iron calcium aluminum garnet,mainly calcium aluminum garnet.It can be divided into three stages:(1)the first stage is early skarn stage(i.e.dry skarn stage),the garnet is related to pyroxene and wollastonite;(2)The second stage is from the end of early skarn stage to late skarn stage(i.e.dry skarn stage to wet skarn stage),the garnet is related to Vesuvianite;(3)The third stage is late skarn stage(i.e.wet skarn stage),the garnet is related to chlorite.From the first stage to the third stage,the component of calcium iron garnet decreases gradually,and the component of calcium aluminum garnet increases gradually,which is closer and closer to the end element of calcium aluminum garnet.(2)The characteristics of Garnet Ring Belt in Zhuxi tungsten deposit are obvious,showing the alternating phenomenon of light and dark ring belt in the backscatter diagram.Its brightness is positively correlated with Fe content and negatively correlated with Al content.From the center to the edge of garnet,the contents of Fe and Al show rhythmic changes,one changes and the other changes,which show two characteristics:(1)The overall content of Al is higher and the overall content of Fe is lower,and the changes of them from the center to the edge are small;(2)Al is enriched and depleted in the center,Fe is enriched and depleted in the edge.The change of the composition of the annulus is mainly controlled by external factors such as the composition of the heating fluid system,garnet with gentle ring composition change is mainly associated with Fushan stone,and garnet with significant ring composition difference is mainly associated with pyroxene,suggesting that the hydrothermal environment is relatively stable during Vesuvianite precipitation,while the hydrothermal conditions are relatively turbulent during earlier pyroxene precipitation,which may be related to the strong water rock reaction between fluid and surrounding rock in the early stage.(3)The light rare earth elements of garnet show a trend of enrichment from early to late.Among them,garnet in the first stage and the second stage has a relative loss of light rare earth elements and a slight loss to slightly enriched of heavy rare earth elements.In the third stage(symbiosis with chlorite),light rare earth elements are more enriched than before,and there is no significant fractionation between light and heavy rare earth elements.The variation characteristics of Eu,Sn and U elements in garnet reveal that the oxygen fugacity of fluid gradually decreases from the first stage to the third stage of skarn process.(4)The content of trace elements in garnet is generally low.W is higher in the early stage and significantly lower in the late stage,which may suggest the precipitation of W.Therefore,the content of tungsten in garnet has the potential to be used as a reference index for the exploration of tungsten deposits.