华北克拉通南缘小秦岭金矿区基性脉岩时代及地质意义  

Geological Significance and Geochronology of Paleoproterozoic Mafic Dykes of Xiaoqinling Gold District,Southern Margin of the North China Craton

作　　者：毕诗健[1,2] 李建威[1,2] 李占轲[1,2] 

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,湖北武汉430074 [2]中国地质大学资源学院,湖北武汉430074

出　　处：《地球科学（中国地质大学学报）》2011年第1期17-32,共16页Earth Science-Journal of China University of Geosciences

基　　金：国家重大科研计划"华北克拉通破坏"(No.90814004);国家自然科学基金创新群体基金(No.40521001)

摘　　要：产于太古代-古元古代变质地体中的石英脉型金矿是世界上最重要的金矿类型之一,大多数金矿区内基性脉岩非常发育,空间上与含金石英脉密切相关.但目前对基性脉岩与石英脉型金矿的成因联系尚未取得一致认识.以华北克拉通南缘小秦岭金矿区为例,对典型矿区(东闯、大湖、枪马)采矿巷道内的基性脉岩开展精确的U-Pb年代学研究.4个脉岩样品给出一致的锆石207Pb/206Pb加权平均年龄(1819±10Ma,1σ);1个样品中的黑云母给出了略微年轻的40Ar/39Ar坪年龄(1719.0±21.0Ma,2σ).定年结果表明:(1)小秦岭金矿区内大量基性脉岩形成于古元古代晚期,是华北克拉通东西块体在1.85Ga左右发生碰撞后伸展作用的产物;(2)前人获得的基性脉岩K-Ar和Rb-Sr年龄(187.6～75.9Ma)可能并非脉岩真实侵位年龄,而是代表这些脉岩遭受中生代构造-热事件影响的扰动年龄(或冷却年龄).最新的成矿年代学研究结果表明,小秦岭地区绝大多数金矿床形成于早白垩世130～120Ma,大大晚于上述古元古代基性脉岩的侵位时代,因此两者之间没有成因联系(尽管它们的空间关系十分密切).小秦岭地区是否存在与金矿床同时的晚中生代基性岩浆活动,对于讨论本区金矿床的矿床成因和成矿构造环境非常重要,但本文工作尚不能明确回答这一问题,今后需要对矿区内各期基性脉岩进行系统的同位素定年.Lode gold deposit is the most economically important type of gold deposits worldwide. It commonly occurs in Archean to Paleoproterozoioc metamorphic terrains and has close spatial relationship with mafic dykes. However,it is still in dispute whether mafic dykes and gold mineralization are genetically related. In this paper,we present LA-ICPMS zircon U-Pb and biotite 40Ar-39Ar ages of four mafic dikes samples collected from three major gold deposits （Dongchuang,Dahu and Qiangma deposits） in the Xiaoqinling gold district,southern margin of the North China craton. Four samples yielded a consistent zircon LA-ICPMS age （207Pb/206Pb 1 819±10 Ma） and a slightly younger 40Ar/39Ar plateau age （1 719.0±21.0 Ma） of biotite. Our results suggest that：（1） numerous mafic dikes in the Xiaoqinling gold district formed in Paleoproterozoioc,in an extensional setting after the collision between the eastern and western blocks of the North China craton at ca. 1.85 Ga; （2） previous whole rock K-Ar and Rb-Sr ages （187.6-75.9 Ma） which are significantly younger than our ages represent thermal perturbation （or cooling ages） caused by Mesozoic tectonic-thermal event. Recent geochronological studies show that the majority of gold deposits formed in Early Cretaceous （130-120 Ma） in the Xiaoqinling district. Therefore,the mineralization event had no relationship with Paleoproterozoic mafic dykes although they were spatially associated. However,this study does not rule out the possibility of existence of Mesozoic mafic dykes in the Xiaoqinling area,which may be very important for the understanding of the metallogeny and regional tectonic setting.

关 键 词：基性脉岩 地质年代学 石英脉型金矿 小秦岭金矿区 岩石学 

分 类 号：P571[天文地球—矿物学] P611[天文地球—地质学]