太行山南段铜矿成矿时代厘定及成矿意义

The Determination of Metallogenic Age of Copper Deposits in the Southern Section of Taihang Mountains,Hebei Province and its Metallogenic Significance

太行山南段井陉-内丘一带是河北省重要的铜矿远景区,区内成矿条件优越。已有研究资料多将该区铜矿类型、成矿条件等与山西中条山铜矿富集区进行类比。由于缺少对铜的成矿时代的精确限定,致使无法对区内铜矿床的形成过程及成因进行较为准确的分析,制约着区域铜矿成因类型对比及找矿勘查工作部署。本文以区内桃园铜矿床及酸枣坪、虎寨口、鹿峪和方垴等四个铜矿化点为研究对象,采用Rb-Sr法测试分析了上述铜矿床及矿化点的矿石硫化物。测试结果显示,桃园铜矿不同硫化物对Rb-Sr等时线年龄在1829.6~1840Ma之间,酸枣坪铜矿点的形成时代为1830.7±5.2Ma,虎寨口铜矿点的形成时代为1844.3±5.9Ma。上述三个铜矿床(点)矿石硫化物Rb-Sr等时线年龄测试结果表明,在古元古代晚期区内有一次较为强烈的铜矿成矿作用,成矿时限在1830~1844Ma之间。而方垴和鹿峪两个铜矿化点矿石硫化物测年结果与上述三个铜矿床(点)形成时间有较大差异,Rb-Sr等时线测年结果分别为1402±23Ma和1376±37Ma,说明在中元古代长城纪末期区内仍有一次铜矿化作用发生。结合华北地台构造演化过程,太行山南段古元古代晚期第一次铜矿化与山西中条山胡-篦型铜矿形成时代接近,铜矿床的形成与吕梁运动关系密切。由于太行山南段铜矿(点)分布区地处陆内构造环境的晋豫裂陷带,而山西中条山铜矿富集区处于秦岭-大别活动带的北缘的"秦岭古洋"壳向华北地台俯冲环境,构造环境差异可能导致两区在铜矿形成潜力及规模上存在一定差异。与区内第一次铜矿化作用相比,发生在中元古代长城纪末期的第二期铜矿化在成矿规模及强度上均较弱,其成矿动力学机制有待进一步分析确定。

Jingxing Neiniu belt in the southern section of Taihang Mountains, with its excellent metallogenic conditions, has been an important target area for prospecting copper deposits. This study analyzed the previous research data （including ore type and metallogenic condition） and contrasted it with Cu enriched areas in Zhongtiao Mountains. Due to the lacking metallogenic ages of copper deposits for a long time, it is impossible to precisely analyze metallogenic process and genesis of copper deposits, which imposes serious influence on the exploration and deployment of copper deposit in this area. With the Taoyuan Cu deposit and four copper mineralization prospects as our objectives in the study area, authors analyzed ore sulfates from Cu ore deposit and prospects mentioned above using Rb Sr dating. The isotopic age results show that the Taoyuan copper deposits occurred in 18296Ma to 1840Ma, and Sanzaoping and Huzaikou mineralized points are 01837±52Ma and 18443±59Ma, respectively. The Rb Sr isochron dating results of above three copper deposits （or points） show that there is a large scale mineralization in late Paleo Proterozoic, with metallogenic time limit between 1830 Ma 1844Ma. But the mineralization time of Fangnao and Luyu mineralized points respectively are 1402±23Ma and1376±37Ma, which have significantly different from the Taoyuan copper deposit and two copper points. This indicates that another mineralization may occur in the Mesoproterozoic period. Together with the structural evolution of the north China platform, , the first copper mineralization in the south of Taihangshan area occurred in the late Paleoproterozoic period, and this is close to mineralization time of the Hubi type copper deposits. It can be concluded that copper mineralization is closely associated with the Luliang movement. Copper ore deposits in south of Taihangshan area is located in the intracontinental rift tectonic environment, while Cu enriched areas in Zhongtiaoshan just lie in the north margin of Qinling Dabie active belt, where is the subduction zone of Qinling paleooceanic to the north China platform. The difference in tectonic settings may lead to large differences in potential and scale of copper mineralization. Compared with the first copper mineralization period, the second one occurring in the Mesoproterozoic period is relatively weak in both scale and mineralization. Its metallogenic dynamics mechanism needs further study.