石榴子石的LA-ICP-MS面扫描U-Th-Pb定年——以铜绿山大型Cu-Fe-Au矽卡岩矿床为例  

U-Th-Pb dating of garnet based on LA-ICP-MS mapping technology:A case study of the Tonglvshan large-scale Cu-Fe-Au skarn deposit

作　　者：葛粲[1,2,3] 汤笑伟 汪方跃[1,2,3] 李修钰[4] 孙贺 顾海欧 袁峰[1,2,3] 郑辉 GE Can;TANG XiaoWei;WANG FangYue;LI XiuYu;SUN He;GU HaiOu;YUAN Feng;ZHENG Hui(School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,China;Laboratory of Three-Dimension Exploration for Mineral District,Hefei University of Technology,Hefei 230009,China;Anhui Province Engineering Research Center for Mineral Resources and Mine Environments,Hefei University of Technology,Hefei 230009,China;Geological Survey of Anhui Province,Hefei 230001,China)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]合肥工业大学矿集区立体探测实验室,合肥230009 [3]合肥工业大学,安徽省矿产资源与矿山环境工程技术研究中心,合肥230009 [4]安徽省地质调查院,合肥230001

出　　处：《岩石学报》2023年第10期2879-2894,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42273061、91962218、42273065);国家重点研发计划项目(2022YFC2903503)联合资助.

摘　　要：矽卡岩矿床的年代学信息对研究矽卡岩矿床的矿床成因、演变过程、成矿规律和找矿勘查具有重要的指示意义。石榴子石是矽卡岩矿床中的常见矿物,它具有一定的U含量,但是由于其普通铅高以及铀分布不均一的原因,导致激光剥蚀电感耦合等离子体质谱仪(LA-ICP-MS)点分析获得年龄成功率不高。针对点分析定年遇到的深度分馏和剥蚀点选取、普通铅校正等问题,本文提出一种利用LA-ICP-MS面扫描分析数据的虚拟点构建技术,在Tera-Wasserburg(TW)图中实现普通铅校正来确定含普通铅石榴子石年龄。通过理论推导、数值模拟和实验分析研究发现,利用相关联的^(208)Pb、^(232)Th、^(238)U测量数据校正生成^(208)Pb_(c)/^(238)U指标并据此对TW图中的数据进行数据分组抽样构造虚拟测量点,可以有效地把面扫描测量数据转换为与点分析测量类似但放射母子比例展布更优的数据。利用此方法对长江中下游成矿带鄂东矿区铜绿山大型Cu-Fe-Au矽卡岩矿床石榴子石进行面扫描分析。仅使用15min的样品面扫描数据,在获得了微量元素含量分布的同时,也获得了同位素比值虚拟点,交点年龄为139.2±2.9Ma(MSWD=0.7,n=126),与前人矿床研究结果相一致,验证了此方法的可行性。利用LA-ICP-MS面扫描定年技术不仅可以获得样品元素含量的二维分布图,有利于对样品期次的筛选,剔除包裹体等异常数据;还可以避免点分析中深度分馏和繁复的选点流程及二次分析等步骤,在获得样品元素含量分布的同时获得矿物年龄,为当前矽卡岩型矿床相关的关键金属研究提供了更为便捷的方法。The chronological information of skarn deposits is of great significance to the study of the genesis,evolution,metallogenic regularity and prospecting of skarn deposits.Garnet is a common mineral in skarn deposits,and is characterized by high U,however,its high common lead and uneven U distribution make it difficult to obtain ages for Laser Ablation Inductively Coupled Plasma Mass Spectrometer(LA-ICP-MS)spot analysis.In order to solve the problems and difficulties of downhole fraction correction and ablation analysis spots selection,we propose a virtual spot construction technique using LA-ICP-MS mapping analysis data to implement common lead correction in Tera-Wasserburg(TW)diagrams to determine the age of common lead-bearing garnets.Through theoretical derivation,numerical simulation and experimental analysis,this paper finds that the corrected ^(208)Pb_(c)/^(238)U index which is generated by ^(208)Pb,^(232)Th,^(238)U associated measurement data can be used to group and resample data in Tera-Wasserburg(TW)diagram and convert mapping data into virtual spot data,which is similar to the LA-ICP-MS spot analysis data,but with a better radial mother-to-child ratio.This approach is used to analyze the garnet from Tonglvshan Cu-Fe-Au skarn deposit,the Middle and Lower Yangtze River Metallogenic Belt.Trace element mapping and isotopic ratio virtual points were obtained simultaneously after the fifteen minutes mapping experiment,and the age obtained was 139.2±2.9Ma with MSWD=0.7(n=126),which is consistent with the results of previous studies and proves the feasibility of this approach.The use of LA-ICP-MS mapping dating technique not only enables the acquisition of two-dimensional distribution maps of sample elemental contents,which facilitates the selection of sample periods and the elimination of abnormal data such as inclusions;but also avoids the need for depth fractionation and complex point selection processes,as well as secondary analysis steps involved in spot analysis.By obtaining the distribution of sample ele

关 键 词：含普通铅矿物U-Th-Pb定年 LA-ICP-MS面扫描技术 关键金属 石榴子石年代学 矽卡岩 铜绿山 

分 类 号：P575.3[天文地球—矿物学] P597.3[天文地球—地质学]