密西西比河谷型铅锌矿床成矿年代学研究进展:兼论金顶矿床成矿年龄分歧  

Research advance in geochronology of the Mississippi Valley-type Pb-Zn deposits:Debate on the metallogenic age of the Jinding deposit

作　　者：王长明[1,2] 段泓羽 李超[3] 祝佳萱 石康兴 陈奇 刘俐君 钱金龙 WANG ChangMing;DUAN HongYu;LI Chao;ZHU JiaXuan;SHI KangXing;CHEN Qi;LIU LiJun;QIAN JinLong(School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;National Research Center for Geoanalysis,Beijing 100037,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [3]国家地质实验测试中心,北京100037

出　　处：《岩石学报》2022年第6期1577-1594,共18页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2020YFA0714802);国家自然科学基金项目(41872080、92162101)联合资助.

摘　　要：金属矿床精确定年仍是国内外科学研究的难题,妨碍了对成矿规律的认识和资源勘探目标的优选评价。针对密西西比河谷型(MVT)铅锌矿床,前期有人分别利用Re-Os法、U-Pb法、^(40)Ar-^(39)Ar法、Rb-Sr法、Sm-Nd法、古地磁测年法和裂变径迹法等不同手段对其成矿时代进行了探索性尝试。其中,Re-Os同位素测年技术虽然仍是疑难金属矿床直接定年的有效手段,但现有Re-Os同位素定年技术还达不到锆石U-Pb法的精度水平。本文以三江特提斯兰坪盆地金顶铅锌镉铊矿床为研究对象,在精细解剖矿床的基础上,开展单阶段硫化物精确识别和高纯提取,建立不同阶段硫化物矿物学标志。前期研究侧重于金顶矿床脉石矿物和黄铁矿等非直接成矿矿物的定年,且年龄变化范围较大(114~23Ma),难以对该矿床的形成时代给出精确的制约;为此,本文对该矿床的成矿矿物开展了高精度定年。5件闪锌矿矿物的Re-Os等时线年龄为129±10Ma(MSWD=126,n=5),对应成矿时代早于古新统云龙组和白垩系景星组赋矿围岩,尚不能代表真实的铅锌成矿时代。闪锌矿测年结果可能受富含Re和Os的有机质的影响。随着同位素地质年代学持续的发展与革新,加之高纯提取方法不断进步,精确定年为MVT铅锌矿床研究提供了更多的技术支撑。Precise geochronology of metalliferous deposits is of critical significance for the understandings of metallogenic regularity and the optimization and evaluation of resource exploration targets,however,it is very difficult.In previous studies,exploratory attempts were applicated in Mississippi Valley-type(MVT)Pb-Zn deposits by using different dating methods,such as Re-Os isotopic chronology,U-Pb geochronology,^(40)Ar-^(39)Ar isotopic age,Rb-Sr dating,Sm-Nd isochron age,paleomagnetic dating,and fission track ages.Re-Os isotopic chronology is still an effective method to directly date the age of knotty metalliferous deposits,although it cannot reach the currently available high-precision level compared with zircon U-Pb geochronology.Taking the Jinding Pb-Zn-Cd-Tl deposit in the Lanping Basin of the Sanjiang Tethys as an example,this study focuses on the accurate identification and high-purity extraction of single-stage sulfide,and establishes the mineralogical indicators of sulfides in different stages based on the fine dissection of the deposit.Previous studies mainly used gangue minerals,pyrite,and other indirect metallogenic minerals for dating of the Jinding deposit,and the ages varied widely and concentrated in 114~23Ma.This study presents high-precision dating of metallogenic minerals,and the Re-Os isochron age of five samples of sphalerite is 129±10Ma(MSWD=126,n=5)which is earlier than the age of host rocks of the Cretaceous Jingxing Formation and the Paleocene Yunlong Formation.The age of 129Ma cannot represent the real metallogenic age of Pb and Zn,and it may be related to the Re-and Os-rich organic matter.Along with the development and innovation of isotopic geochronology and the progress of high-purity extraction methods,precise dating would provide more key supports for the geochronology research of the MVT Pb-Zn deposits.

关 键 词：MVT矿床 定年方法 闪锌矿Re-Os定年 金顶矿床 

分 类 号：P597[天文地球—地球化学] P618.42[天文地球—地质学] P618.43