Genesis relationship between magma evolution and two types of tungsten mine-ralization in Yaogangxian deposit:Evidence from biotite and garnet chemistry
The Yaogangxian W deposit in the Nanling region hosts quartz vein-type wolframite orebody and skarn-type scheelite orebody,which both reach large scale sizes and together to make this deposit to be one of the largest W deposits around the world.Both quartz-vein-and skarn-type orebodies occur in the contact zones between the Yaogangxian granitic complex and the country rocks.The Yaogangxian complex massif mainly consists of medi-um-grained biotite monzogranite and fine-grained two-mica monzogranite,but the genetic relationship between multi-stage magmatic evolution and different types of tungsten mineralization has been debated intensively.In this study,we examined the geochemical characteristics of biotite and garnet from the medium-grained biotite monzogranite and fine-grained two-mica monzogranite,in order to figure out chemical conditions during the for-mation of different granitic phases.Biotite from the fine-grained two-mica monzogranite has lower XMg value,closer to Fe2+ end members,lowerⅣ(F)and higher log(f HF/f HCl)fluid value than that from the medium-grained bi-otite monzogranite,indicating that the former formed in more reduced environment with higher F contents com-pared to the latter.Garnet from both phases are typical magmatic origin,and are in spessartite compositions.MnO contents in garnet grains increase with the decrease of CaO,FeO,and MgO contents,and Mn/(Mn+Fe)values,and Sc,Zn,Y,and HREE concentrations gradually increase with the decrease of MgO contents from medium-grained biotite monzogranite to fine-grained two-mica monzogranite,suggesting that the magmatic differentiation of fine-grained two-mica monzogranite is higher than that of medium-grained biotite monzogranite,which is con-ducive to the enrichment of W.The formation of quartz vein-type wolframite and skarn-type scheelite ores are proposed to be characterised by low oxygen fugacity and high F content,which is consistent with that of the fine-grained two-mica monzogranite.Accordingly,in combination of the geophysical,geochemical,and drilling infor-mation,we propose the exploration model for the deep part of the Yaogangxian deposit,and define quartz vein-type wolframite prospecting target in the deep Dagenlong area,greisen-type W prospecting target in the deep Yan-meiling area,and skarn-type scheelite prospecting target in the southeast of the Heshangtan area.
biotitegarnetoxygen fugacityvolatilesfractional crystallizationexploration modelYao-gangxian W deposit
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