Most economically important tungsten(W)deposits are of magmatic-hydrothermal origin.The species and partitioning of W during fluid exsolution,considered to be the controlling factors for the formation of ore deposits,are thus of great significance to investigate.However,this issue has not been well addressed mainly due to the significant difference in reported partition coefficients(e.g.,from strongly incompatible to strongly compatible)between fluid and melt(DWfluid/melt)Here,we used an in situ Raman spectroscopic approach to describe the W speciation,and to quantitatively determine the Dfluid/melt of individual and total W species in granite melts and coexisting Na2WO4 solutions at elevated temperatures(T;700-800℃)and pressures(P;0.35-1.08 GPa).Results show that WO42-and HWO4 are predominant W species,and the fractions of these two species are similar in melt and coexisting fluid.The partitioning behaviors of WO42-and HWO4-are comparable,exhibiting strong enrichment in the fluid.The total DWfluid/melt ranges from 8.6 to 37.1.Specifically,DWfluid/melt decreases with rising T-P,indicating that shallow exsolution favors enrichment of W in evolved fluids.Furthermore,Rayleigh fractionation mod-eling based on the obtained DWfluuid/melt data was used to describe the fluid exsolution processes.Our results strongly support that fluid exsolution can serve as an important mechanism to generate W-rich ore-forming fluids.This study also indicates that in situ approach can be used to further investigate the geo-chemical behavior of ore-forming elements during the magmatic-hydrothermal transition,especially for rare metals associated with granite and pegmatite.

Ye Qiu;Xiaolin Wang;Jianjun Lu;I-Ming Chou;Ye Wan;Rongqing Zhang;Wenlan Zhang;Rui Sun

State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China;Frontiers Science Center for Critical Earth Material Cycling,Nanjing University,Nanjing 210023,China;Key Laboratory of Experimental Study under Deep-sea Extreme Conditions,Institute of Deep-sea Science and Engineering,Chinese Academy of Sciences,Sanya 572000,China;Department of Geology,Northwest University,Xi'an 710069,China

科学通报（英文版）

[1]Ye Qiu;Xiaolin Wang;Jianjun Lu;I-Ming Chou;Ye Wan;Rongqing Zhang;Wenlan Zhang;Rui Sun-.In situ observations of tungsten speciation and partitioning behavior during fluid exsolution from granitic melt)[J].科学通报（英文版）,2022(22):2358-2368

DWfluid,Dfluid,WO42,HWO4,DWfluuid

In,situ,observations,tungsten,speciation,partitioning,during,exsolution,from,granitic,Most,economically,important,deposits,magmatic,hydrothermal,origin,species,considered,controlling,factors,formation,thus,great,significance,investigate,However,this,issue,has,not,been,well,addressed,mainly,due,significant,difference,reported,coefficients,strongly,incompatible,between,Here,used,Raman,spectroscopic,approach,describe,quantitatively,determine,individual,total,granite,melts,coexisting,Na2WO4,solutions,elevated,temperatures,pressures,GPa,Results,show,that,predominant,fractions,these,two,similar,behaviors,comparable,exhibiting,enrichment,ranges,Specifically,decreases,rising,indicating,shallow,favors,evolved,fluids,Furthermore,Rayleigh,fractionation,mod,eling,obtained,data,was,processes,Our,results,support,serve,mechanism,generate,forming,This,study,also,indicates,further,geo,chemical,elements,transition,especially,rare,metals,associated,pegmatite

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