河北省东坪金矿钾质蚀变岩中的两期锆石年代学研究及意义  

Two Stage Zircon U-Pb Ages of the Potash Altered Rock in the Dongping Gold Deposit,Hebei Province,and Their Geological Implications

作　　者：李长民[1] 邓晋福[1] 苏尚国[1] 李惠民[2] 刘新秒[2] 

机构地区：[1]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 [2]天津地质矿产研究所,天津300170

出　　处：《地球学报》2010年第6期843-852,共10页Acta Geoscientica Sinica

基　　金：国家自然科学基金重点项目(编号:40234048);全国重要矿产成矿地质背景研究(编号:1212010633902)和;中国地质大学地质过程与矿产资源国家重点实验室项目(编号:GPMR0735)联合资助;973项目(2006CB403508)

摘　　要：河北省崇礼县东坪金矿位于水泉沟碱性杂岩体内,金矿石包括低硫化物石英脉型和钾质蚀变岩型两种类型。本次工作我们对采自东坪金矿70号脉深部的钾质蚀变岩中的锆石进行了成因矿物学和成矿年代学研究,结果表明,矿脉中的锆石可以分成岩浆锆石和热液锆石两种成因类型。岩浆锆石具有自形到半自形结构,在背散射电子图像(BSE)上呈暗灰色,在阴极发光图像(CL)上具有明显的岩浆振荡环带,锆石U-Pb加权平均年龄为382.8±3.3 Ma。热液锆石多呈不规则状充填在岩浆锆石中,在BSE图像上呈亮灰白色,在CL图像上为深黑色(无阴极发光),锆石的Th、U含量和Th/U比值较岩浆锆石明显增高,锆石U-Pb加权平均年龄为140.3±1.4 Ma,说明东坪金矿形成于早白垩世。140 Ma成矿年龄的发现,为认识河北省东坪金矿的成矿时代提供了新证据,具有重要的地质意义。Located in Chongli County of Hebei Province,the Dongping gold deposit is hosted by the Shuiquangou alkaline complex.There are two types of gold ores in this ore deposit,namely the low-sulfide quartz veins and the intense k-feldspar alteration type.In this paper,the authors made a mineralogical and U-Pb geochronologic study of the zircons from the intense k-feldspar alteration of No.70 vein.Two types of zircons were recognized,i.e.,magmatic and hydrothermal ones.The magmatic zircons are characterized by euhedral-subhedral crystals,dark gray color on the backscattered electron（BSE） image,and clear magmatic oscillatory zoning on cathodelumines-cence（CL） image.The U-Pb analytical data of the magmatic zircons indicate a weighted mean 206Pb/238U age of 382.8±3.3 Ma.The hydrothermal zircons are mainly of irregular form filled with magmatic zircons.The hydro-thermal zircons show light grayish white color on the BSE image and dark black color（non-luminescent） on the CL image.Compared with the magmatic zircons,the hydrothermal zircons have much higher Th,U content and Th/U ratios.The LA-ICP-MS zircon U-Pb age is 140.3±1.4 Ma.It is suggested that the Dongping gold deposit formed in the early Cretaceous.The discovery of the 140 Ma ore-forming age provides new evidence for the met-allogenic epoch of the Dongping gold deposit.

关 键 词：钾质蚀变岩 锆石U-PB定年 岩浆锆石 热液锆石 东坪金矿 河北省 

分 类 号：P618.51[天文地球—矿床学] P588.32[天文地球—地质学]