摘要
锆石特征较好地记录了形成环境,可以指示其成因类型,反演寄主岩石岩浆的演化过程。本文利用阴极发光和LA_ICPMS技术获得了江西大岭上钨矿区花岗斑岩锆石的阴极发光图像、微量元素数据。研究表明该花岗斑岩中的锆石包括无核燕山期岩浆锆石、继承锆石和被捕获锆石。无核锆石阴极发光图像暗黑,Th/U<0.1,LREE/HREE比值高,Ce弱正异常,平均锆石Ti温度计地质温度为872℃,兼具岩浆锆石和热液锆石的特征,为形成于伟晶岩阶段之前的富含热液的岩浆晚期阶段的岩浆锆石。捕获锆石整体具灰白阴极发光,其裂隙中见暗黑阴极发光,Th/U>0.4,LREE/HREE值低,Ce正异常,锆石Ti温度计地质温度为766℃,为典型的岩浆锆石。继承锆石的核具有灰白色阴极发光,其边缘阴极发光暗黑,锆石微量元素特征值介于前两类锆石之间,其核部为形成于燕山期之前的岩浆锆石,其边部为与无核锆石同时形成的锆石边。区域上形成于燕山期之前的岩浆岩仅有晋宁期花岗闪长岩,因此捕获锆石和继承锆石核可能来源于晋宁期花岗闪长岩。晋宁期花岗闪长岩可能是黑云母花岗斑岩的一种源岩。无核锆石特征说明,该类锆石结晶时,寄主岩石岩浆处于富含高温热液、压力降低的环境中,岩浆演化处于伟晶岩阶段之前的岩浆晚期阶段。该阶段的这种富含热液的岩浆具有很强的金属运载能力,值得进一步研究。
The features of zircons are obviously controlled by their formation environment and can be used to verify their origin and the evolution process of the host rock magma.The authors studied the trace elements and genesis of the zircons from the granite porphyry in the Dalingshang tungsten deposit of Jiangxi Province and investigated the magma evolution process by means of cathodoluminescence and LA-ICPMS.The Dalingshang tungsten deposit is an important deposit inthe Dahutang ore concentration area.It is a superlarge W-Cu-Mo polymetallic deposit found in 2010.The mineralization of the Dalingshang tungsten ore deposit was closely related to the granite porphyry,but the zircons in the granite porphyry have not been studied in detail yet.Yanshanian magmatic zircons,inherited magmatic zircons and captured zircons were found in the granite porphyry in the Dalingshang tungsten deposit.The Yanshanian magmatic zircons seem to be the typical hydrothermal zircons with the features of non-cathodoluminescence,low Th/U ratios （＜ 0.1）,relative enrichment of LREE and weak positive anomaly of Ce.Nevertheless,they also display the characteristics of both hydrothermal zircons and magmatic zircons,with some samples falling in the hydrothermal zircon area whereas others in the magmatic zircon area in the diagrams of （Sm/La）N-La,δCe-（Sm/La）N,and δCe-δEu and（Sm/La）N-（Lu/Gd）N.Yanshanian magmatic zircons should be a part of magmatic zircons,as shown by the fact that their average zircon Ti thermometer geological temperature is 872 ℃ and their host rocks are relatively fresh hypabyssal intrusive rock.It is thought that the zircons in pegmatite have features of hydrothermal zircons but no features of magmatic zircons.Compared with the features of zircons in pegmatite,the Yanshanian magmatic zircons should beconsidered to have been formed before the pegmatite stage.According to all features mentioned above,the authors have arrived at the conclusion that the Yanshanian magmatic zircons in the study area should be classified as the magmatic zircons formed in the magma with rich hydrothermal fluids before the pegmatite stage.The magma rich in hydrothermal fluids could contain a lot of metals that formed the metal deposit late,and hence researchers should pay more attention to the magma so as to find more information about the ore deposit.The captured zircons show uneven lighting gray and white CL images with some non-cathodoluminescence edges in the cracks of the zircons.The captured zircon has high Th/U ratios （＞ 0.4）,relatively low LREE/HREE and positive anomaly of Ce.In the diagrams of （Sm/La）N-La,δCe-（Sm/La）N,and δCe-δEu and （Sm/La）N-（Lu/Gd）N,the captured zircons all fall in the magmatic area.The zircon Ti thermometer geological temperature is 766 ℃.All features point to the conclusion that the captured zircon should be the magmatic zircon and its formation was controlled by Jinningian magmatism.The study of the regional geological condition has revealed that the captured zircon must have only come from the granite diorite of Jinning Period because the granite diorite of Jinning Period was the unique magma product in Jinningian period in the study area.The cores of inherited zircons show gray and white cathodoluminescence and their edges have no cathodoluminescence.Their ratios of Th/U and LREE/HREE are between those of the Yanshanian magmatic zircons and the captured zircons.In the diagrams of （Sm/La）N-La,δCe-（Sm/La）N,and δCe-δEu and （Sm/La）N-（Lu/Gd）N,all inherited zircons are in the area between magmatic zircons and hydrothermal zircons.Their average zircon Ti thermometer geological temperature is 744℃.The inherited zircon cores have the same properties as the captured zircons and their new zircon edges have the same properties as the Yanshanian magmatic zircons.So it is reasonably considered that the granite diorite of Jinning Period was one of the original rocks of the granite porphyry rock.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2014年第5期811-824,共14页
Acta Petrologica et Mineralogica
基金
国家科技支撑计划项目(2011BAB04B02)
教育部核资源与环境重点实验室开放基金项目(NRE1209)
关键词
锆石微量元素
锆石成因类型
花岗斑岩
地质意义
大岭上钨矿
江西
trace elements of zircon
zircon origin
granite porphyry
geological significance
Dalingshang tungsten deposit
Jiangxi
