中条山涑水杂岩的同位素年代学研究及其地质意义

中条山是中国重要的铜多金属成矿带,拥有著名的晚太古代“变斑岩型”铜矿峪大型铜矿床和元古代“层控型”胡家峪—篦子沟铜矿床,近年来又在中条山西南段的涑水杂岩中发现以变基性火山岩(斜长角闪岩)为容矿岩石的桃花洞铜矿。为了弄清楚该铜矿的形成时代及其成矿地质背景,利用电感耦合等离子质谱(LA-MC-ICP-MS)方法对桃花洞铜矿容矿围岩—涑水杂岩中的寨子—西姚灰色片麻岩、斜长角闪岩及二长花岗岩进行了同位素年代学研究。结果表明:寨子—西姚灰色片麻岩、斜长角闪岩脉和二长花岗岩中锆石的岩浆结晶年龄分别为(2 625±11)、(2 592±16)、(2 548±15)Ma; 岩石中古老继承性锆石的年龄分别为(2 790±15)、(2 773±24)、(2 782±34)Ma; 三种不同成生顺序的岩石中均有大于2 700 Ma的锆石存在,且年龄相当接近; 中条山地区涑水杂岩可能最初形成于太古代。涑水杂岩作为与成矿关系密切的容矿围岩,其成岩时代可以间接指示成矿时代,由此得出赋存在变基性火山岩层中的古火山含矿原岩建造型铜矿有可能是中国最古老的铜矿之一。

Isochronology study on Sushui Complex in Zhongtiao Mountains and its geological significance

Zhongtiao Mountains are the important copper-polymetallic ore belts in China, producing famous large scale Tongkuangyu copper deposit with metamorphotic porphyry type formed in upper Archaeozoic and Hujiayu-Bizigou copper deposit with stratabound type formed in Proterozoic. Recently, Taohuadong copper deposit of ore-bearing rock hosted in meta-basic volcanic rock(amphibolite)was discovered in Sushui Complex which located in the southwestern segment of Zhongtiao Mountains. In order to determine the ore-forming epoch and geological background for Taohuadong copper deposit, Zhaizi-Xiyao grey gneiss, amphibolite and monzogranite in Sushui Complex, which were ore-bearing wall rocks in Taohuadong copper deposit, were used for isotope dating by the method of LA-MC-ICP-MS. The results showed that the magmatic crystallization ages of zircons were(2 625±11),(2 592±16),(2 548±15)Ma, respectively; the ages of older inherited zircons were(2 790±15),(2 773±24),(2 782±34)Ma, respectively; all the three rocks crystallized in different times had the inherited zircons with similar ages, which were more than 2 700 Ma; Sushui Complex in Zhongtiao Mountains might be initially formed in Archaeozoic. The diagenesis age of Sushui Complex, which was the ore-bearing rock related with metallogenic association, could indirectly indicate the mineralogenetic epoch, so that the ore-bearing palaeovolcano copper deposit with construction type hosted in meta-basic volcanic rock could be one of the oldest copper deposits in China.