摘要
新田岭矿床是典型的矽卡岩型白钨矿床,与侏罗纪花岗岩侵入体有关,查明其成矿流体演化历史,对于探讨新田岭矿床成因和理解钨矿床成矿过程具有重要意义。以新田岭矿床普遍存在的矽卡岩矿物——石榴子石为研究对象,运用扫描电镜、EPMA和LA-ICP-MS等技术对石榴子石的结构、主微量元素和U-Pb年龄进行分析。根据石榴子石在背散射图像下显示的结构特征,可将新田岭矿床中的石榴子石划分为3个世代:早阶段为暗色石榴子石(Grt1);中阶段为具有明显震荡环带的石榴子石(Grt2),可划分为细环带(Grt2-1)和粗环带(Grt2-2);晚阶段为亮色石榴子石(Grt3)。通过对Grt2进行LA-ICP-MS U-Pb定年分析,确定其成岩年龄为(159.5±3.0)Ma,与该地区细粒斑状黑云母花岗岩的成岩时代(164~157 Ma)在分析误差范围内基本一致。Grt1、Grt2-1和Grt3均具有轻稀土亏损、重稀土富集的“左倾型”稀土配分模式,其中Grt1具有较明显的Eu负异常,Grt2-1具有较弱的Eu负异常,Grt3具有微弱的Eu负异常;Grt2-2具有轻重稀土亏损、中稀土富集的“驼峰型”配分模式,具有较弱的Eu正异常。从Grt1到Grt3,石榴子石中Mn、W含量呈现先下降后上升的变化趋势,Grt3中的W含量高于Grt2但低于Grt1。新田岭矿床石榴子石的稀土配分模式与微量元素组成表明,该矿床的成矿作用经历了多阶段热液过程,石榴子石形成过程中流体的氧逸度和温度先升高后降低,压力和pH值先降低后升高。此外,石榴子石中的钨含量变化暗示着新田岭矿床中钨矿化主要发生在退变质阶段,而白钨矿形成后在退变质晚期可能经历了溶解—再沉淀的过程。
The Xintianling deposit is one of the largest skarn-type scheelite deposits in South China,and its mineralization has undergone complex magmatic and hydrothermal processes.Taking the skarn garnet in the Xintianling deposit as the research object,the U-Pb dating,in-situ major and trace element analysis of garnet were carried out by EPMA and LA-ICP-MS in-situ micro-area testing techniques.The U-Pb dating reveals thatthe age of ore-related garnet in Xintianling deposit is ca.(159.5±3.0)Ma,which is consistent with that of thefine-grained porphyritic biotite granite(164~157 Ma)of the Qitianling rock mass,indicating that the Xintianlingtungsten mineraliztion is closely related to the Qitianling rock mass. Based on the mineral assemblages andbackscattering images,it is determined that there are three generations of garnet in the Xintianling tungstendeposit. According to the structural characteristics of garnets in the backscattered images,the garnets in theXintianling deposit can be divided into three generations,namely,the early stage dark garnet(Grt1),the middlestage garnet with obvious oscillation zone(Grt2) and the late stage bright garnet (Grt3).Among them,Grt2 canbe divided into Grt2-1 with oscillatory zones and Grt2-2 with thick oscillatory zones.Grt1,Grt2-1and Grt3 showthe left-skewed REE patterns with LREE depleted and HREE enrichment. Grt1 has an obvious negative Euanomaly,Grt2-1 has a weak Eu negative anomaly,and Grt3 has a weak Eu negative anomaly.In contrast,Grt2-2has a“ hump-type” REE pattern with LREE enrichment and HREE depleted,and the weak Eu positive anomaly.From Grt1 to Grt3,the content of Mn in garnet showes a trend of first decreasing and then rising,and the Wcontent in Grt3 is higher than Grt2 but lower than Grt1.These results suggest that the Xintianling deposit hasexperienced multiple hydrothermal processes,and the oxygen fugacity and temperature of the ore fluid firstincreas and then decreases,and the pressure pH value first decreases and then increases during the ore-formingprocesses. Combined with the variations of W content in garnet from different mineralization stages,it isconsidered that the mineralization of tungsten in the Xintianling deposit mainly occurs in the retrogrademetamorphic stage,and undergoes the process of dissolution-reprecipitation in the late retrograde metamorphicstage.
作者
李博
邹少浩
许德如
陈喜连
王雪娜
王华
LI Bo;ZOU Shaohao;XU Deru;CHEN Xilian;WANG Xuena;WANG Hua(State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,Jiangxi,China)
出处
《黄金科学技术》
CSCD
2023年第2期232-251,共20页
Gold Science and Technology
基金
国家自然科学基金项目“江南古陆金(多金属)大规模成矿的机理研究”(编号:41930428)
“胶体金的稳定性及其对金富集成矿的作用:以豫西吉家洼金矿床为例”(编号:42002089)
江西省自然科学基金项目“岩浆热液过程中铌钽差异性富集机理研究——以江西省宜春Ta-Nb矿床和黄山Nb-Ta矿床为例”(编号:20224BAB203036)联合资助。
