Evolution Process Of Ore-forming Fluids In Maoping Quartz Vein Type Tungsten Deposit,Jiangxi Province

Mica and wolframite coexist closely in tungsten deposits.Both mica and wolframite can reflect the origin and evolution of ore-forming fluids.There are a large number of wolframite quartz vein tungsten deposits in southern Jiangxi.Wolframite is the main object of industrial direct mining and utilization.Previous studies on wolframite deposits have focused on the analysis of major and trace elements in rocks related to wolframite genesis,diagenetic and metallogenic age,temperature and salinity and hydrogen and oxygen isotopes of quartz fluid inclusions.This paper is different from the traditional wolframite research.From the perspective of mineralogy,wolframite and mica are regarded as a system.According to the mineralization type of wolframite,the coexisting mica and wolframite are systematically collected from deep to shallow,and the major and trace elements of mica and wolframite are obtained by electron probe and LA-ICP-MS,and the variation rules of elements in space are analyzed,so as to invert the evolution process of ore-forming fluid.The Maoping tungsten deposit,a typical quartz-vein type tungsten deposit,is located in the Nanling W-Sn metallogenic province of southern China.The mineralization types are greisen(type ?)and wolframite-quartz vein(type ?).Both greisen and wolframite-quartz veins are mainly composed of quartz,mica and wolframite.Wolframite of type ? have higher Sn,Nb,Ta and REE concentrations than type ?.Wolframite of Type I has significantly negative Eu anomaly,while type ? has slightly negative Eu anomaly from deep to shallow,and even turn into positive Eu anomaly on the ground.Two stages of wolframite formation in greisen(type ?)can be identified by SEM.The wolframite of greisen(type ?)was subdivided into type ?a(dark part)and type ?b(light part)according to the WO3,Nb and Ta contents.Type ?a has lower WO3 and higher Nb-Ta contents than Type ?b.From type ?a to type Ib,the Fe/(Fe+Mn)ratio decreases relatively.The Fe/(Fe+Mn)ratios of wolframite in greisen range from o.4 to 0.6,showing a trend of increasing Mn in wolframite from core to rim.Wolframite-quartz vein(type ?)might inherit the Mn-rich tendency in the beginning.The micas of Maoping deposit can be classified into four types according to geological occurrence and chemical composition difference.The micas of granite are protolithionite and Li-phengite.The micas of greisen are zinnwaldite and Li-phengite.The mica shell of wolframite-quartz veins(except mica in the ground)are zinnwaldite.The micas in the veinlet of ground are phengite which are subdivided into Fe-poor phengite and Fe-rich phengite.In the greisen,Li-phengite replace zinnwaldite.W shows negative correlation with Nb and Ta,The process of greisenization maybe is the beginning of tungsten enrichment.Tungsten,Sn,Nb and Ta are from magmatic fluids,while Co,Ni,V and Ti maybe come from fluid leaching extraction of elements in strata.The mica and wolframite have similar variations trend in Sn,Nb,Ta,Mg,Co,Ni,V and Ti.From deep to ground,the contents of Sn,Nb,Ta gradually decrease while Mg,Co,Ni and V gradually increase.The Fe3+/(Fe3++Fe2+)ratios of wolframite and mica reflect the similar trend of the oxygen fugacity variation of ore-forming fluids,which decrease in the early and then increase.The content of Mo in mica decreases from-5m,which is related to the precipitation of Molybdenite from-5m.The content of Zn in mica decreases from-75m,which is related to the precipitation of sphalerite from-75m.The decreasing of Zn and Mo contents of micas indicates the precipitation of molybdenite and sphalerite precipitation during the emplacement of ore-forming fluids.