Study On The Fluid Inclusions Of The Fujiawu Porphyry Cu Deposit, Dexing, Jiangxi Province

Fujiawu is one of the copper porphyry deposits in the Dexing ore field which is composed of Tongchang,FuJiawu and Zhushahong.Based on the fine anatomy of the Fujiawu deposit,the metallogenic geological features,including main alteration and mineralization types,the order of the formation of mineral veins and the different mineral assemblages(A,B and D veins)of the deposit are studied,to establish the alteration and mineralization zoning model.By EPMA the trace elements of metal minerals in various vein bodies,the change of trace elements in each phase body and the metal minerals deposited by trace elements are analyzed.Study of the detailed fluid inclusions in various vein bodies,is carried out to reconstruct the evolution process of ore-forming fluid and to discuss the precipitation mechanism of ore-forming material.The alteration zoning of Fujiawu is similar to other porphyry deposit in arc settings belt.Timely,the alteration changes from potassic and propylitization alterations in early time,to phyllic alteration and argillization alteration in transitional phase.According to the mineralization characteristics,11 types of veins of the A-type vein,Btype vein and D-type vein are identified in the Fujiawu deposit.According to the result of fluid inclusions from different veins,the characteristics and evolution of ore-forming fluid are as follows:(1)In the early stage,the four A-type veins were formed when the porphyry rock had not been completely solidified,so that the veins are irregluar and unclearly bordered with wall rock or porphyry rock and large-scale of K-feldspar alteration;Fluid inclusions in A veins demonstrate homogenization temperatures of 360~520? and the salinity of 53.3~64.5%NaCl and 7.7~14.7%NaCl;(2)In the middle stage,the two B-type veins were largely formed.Most of B-type veins are straight and along with the chalcopyrite,molybdenite mineralization.Fluid inclusions in B veins demonstrate homogenization temperatures of 280~460? and salinity of 43.1~53.6% NaCl and 3.2~9.3%NaCl;(3)At the post-minerlization stage,four Dtype veins with or without alterated Hydromica halo were fromed when the mineralizaiton system was opened and meteoric water and undergrand water infused into the open fissure with large py-Q-ser alteration.Fluid inclusions in D veins demonstrate homogenization temperatures of 160~300? and salinity of 1.4~6.0% NaCl.In conclusion,the characteristics of ore-forming fluid of Fujiawu changed from high temperatures,high salinities at early stage to low temperatures,low salinities at later stage.The contents of Au in pyrite and chalcopyrite is higher.From early to late stage,the content of Au in the veins became more and more rich,and the Au content in the B-type and D-type veins was much higher than that of the A-type veins,indicating that Au began to crystallize in the middle and late stages of the mineralization.The content of Ag in galena and chalcopyrite is much higher than that of pyrite and molybdenite.The contents of Ag in the Dtype vein are much higher than those of the A-type and B-type veins,and the small particles of natural silver are visible on the edge of chalcopyrite in the D chalcopyrite-pyrite vein,indicating that Ag has been precipitated in a large amount of crystallization at the later stage of the mineralization.The contents of Se,Ge,Pb,Bi and Co in the D-type vein are much higher than those of the A-type and B-type veins,indicating that these elements began to precipitate at the later stage of mineralization.The contents of As,Zn,Ni and Sb in the B-type and D-type veins were much higher than those in the A-type veins,indicating that these elements began to precipitate and crystallize at the middle-later stage of mineralization.The primary copper mineralization of Fujiawu start at late stage of potassic alteration,and main copper mineralization is firstly in transitional phase,and secondly in the quartzsericite alteration phase.Mo mineralization forms in transitional phase and the quartz-sericite alteration phase.