白钨矿地球化学对皖南竹溪岭和逍遥钨矿成矿流体演化的指示  

Scheelite geochemistry implications for ore-forming fluid evolution of Zhuxiling and Xiaoyao tungsten deposits,southern Anhui Province

作　　者：段晓侠 句英富 王三达 王志强[1] DUAN XiaoXia;JU YingFu;WANG SanDa;WANG ZhiQiang(School of resources and environmental engineering,Hefei Unviersity of Technology,Heifei 230009,China)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《岩石学报》2023年第9期2741-2760,共20页Acta Petrologica Sinica

基　　金：安徽省公益性地质工作项目(2021-g-2-11);国家自然科学基金项目(42072089)联合资助.

摘　　要：近年来赣北-皖南地区陆续发现了一批斑岩-矽卡岩钨矿床,构成一个新的世界级钨成矿带——江南钨矿带。位于该成矿带东北段的皖南地区发育大量与弱分异氧化性花岗岩相关的钨多金属矿床,目前这类矿床缺乏基于矿物原位地球化学的精细研究,成矿流体性质和演化认识不清。本文选取皖南地区两个代表性钨多金属矿床——竹溪岭和逍遥矿床为研究对象,开展白钨矿原位成分分析,揭示矽卡岩体系成矿流体性质、物化条件变化以及水岩反应影响,并探讨江南钨矿带内钨成矿条件差异。白钨矿原位成分分析能够精细厘定矽卡岩形成过程的氧逸度、pH值、温度、成矿流体组成变化以及水岩反应等信息。逍遥矿床和竹溪岭矿床的白钨矿均可分为三个阶段:其中早期进变质矽卡岩中白钨矿(Sch-1)的Mo含量最高,REE表现为轻重稀土分异的右倾曲线,具有负Eu异常,与成矿母岩REE配分类似,指示早期流体是相对富Cl的岩浆出溶热液;Sch-2产于退变质矽卡岩阶段,其轻重稀土分异变弱,有一定的正Eu异常,REE和Mo含量较低,推测早期Sch-1结晶摄取大量的LREE,导致后期流体轻重稀土比值降低;脉状产出的白钨矿(Sch-3)形成于晚期石英-硫化物阶段,其REE、Nb、Ta和Y等元素含量显著高于Sch-1和Sch-2,REE表现为轻重稀土分异弱的平坦型曲线,发育弱正Eu异常,暗示晚期流体更加富F。本文研究认为从早期Sch-1到晚期Sch-3,白钨矿Eu异常变化不一定反映氧逸度变化,而更可能反映的是水岩反应制约;此外,白钨矿的Mo含量相对于Eu异常更能够有效地反映体系的氧逸度特征。与逍遥矿床相比,竹溪岭矿床石榴石的钙铁榴石组分含量较低,锰铝榴石组分含量高,白钨矿Mo含量(630×10^(-6)~18813×10^(-6))显著低于逍遥白钨矿(8700×10^(-6)~74478×10^(-6)),指示竹溪岭矿床相比于逍遥矿床是相对还原的钨矽卡岩体系。前人认为江�In recent years,a batch of porphyry-skarn tungsten deposits have been successively discovered in the northern Jiangxi and southern Anhui area.Those deposits consist of a new world-class tungsten metallogenic belt,which is called the Jiangnan Tungsten Belt.There are a large number of W-Mo deposits related to weakly differentiated oxidative granites in the southern Anhui area in the northeastern part of the belt.Researches on such deposits are relatively limited and lack of studies on their mineral chemistry,and as a result,the nature and evolution of their ore-forming fluids remain unclear.In this paper,two representative tungsten polymetallic deposits in the southern Anhui area,the Zhuxiling and Xiaoyao deposits,are selected to carry out in situ compositional analyses on the scheelite to reveal the nature of mineralizing fluids in the skarn system,the change of physochemical conditions and the influence of water-rock reaction of these two depsoits.We also discussed the differences of the tungsten mineralization chatacteristics between these two deposits and other ones found in the Jiangnan Tungsten Belt.According to our study,the in situ compositional analysis of the scheelites could reflect not only the changes of oxygen fugacity,pH values,temperatures and compositions of the ore-forming fluids,but also the water-rock reaction process during the skarn formation.Furthermore,the scheelites of Xiaoyao and Zhuxiling deposits can be divided into three stages,among which the early-stage scheelite(Sch-1)is formed in the prograde skarn stage and coexists with garnet and diopside,while the Sch-2 happened in the retrograde metamorphic stage of the skarn,and the Sch-3 was formed the late quartz-sulfide stage.The Mo content of Sch-1 is the highest and the REE shows a right-dipping curve with a negative Eu anomaly,which is similar to the REE pattern of the parent rock,indicating that the early fluid was magmatic exsolved Cl-rich fluid.Compared to Sch-1,Sch-2 shows a weaker REE differentiation and positive Eu anomaly,whose RE

关 键 词：白钨矿 逍遥钨多金属矿 竹溪岭钨多金属矿 矽卡岩型矿床 江南钨矿带 

分 类 号：P588.312[天文地球—岩石学] P595[天文地球—地质学] P618.67