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内蒙古白乃庙铜矿床是华北地区知名的大型铜矿床之一,位于兴蒙造山系满都拉-霍林郭勒弧盆系白乃庙早古生代岛弧内。该矿床包括南、北两个矿带,南矿带矿体产于白乃庙组绿片岩中,北矿带矿体产于花岗闪长斑岩内。白乃庙组共划分为五个岩性段,第一、三、五岩段岩性主要为绿泥斜长片岩、阳起绿泥斜长片岩,是白乃庙铜矿的主要赋矿层位;第二、四岩段为长英片岩和变质流纹英安岩组合。白乃庙组地层的原岩为一套中基性-中酸性海相火山-沉积岩组合。对于该矿床及白乃庙组地层的形成时代争议较大,前人多认为二者均形成于中元古代。本文采用锆石SHRIMP U-Pb同位素定年获得了白乃庙组第三岩性段绿泥斜长片岩的形成年龄为439.8±6.7Ma,花岗闪长斑岩的形成年龄为433.9±2.2Ma、451.8±3.0Ma,采用辉钼矿Re-Os同位素分析获得辉钼矿的形成年龄为433.9±3.1Ma。结合前人成果,提出白乃庙组地层及花岗闪长斑岩的成岩时代和白乃庙铜矿的成矿时代均为晚奥陶-早志留世,它们同属早古生代白乃庙岛弧岩浆作用的产物。
The Bai’nai copper deposit in Inner Mongolia is one of the well-known large-scale copper deposits in North China. It is located in the early Paleozoic island arc of the Mandala-Hollingular basin in the Xingmeng orogen. The deposit consists of two ore belts in the south and north. The ore body in the south ore belt is produced in the green schist of the Bai Nimiao Formation and the ore body in the north ore belt is produced in the granodiorite porphyry. The Bai Nai Miao Formation is divided into five lithologic sections. The lithology of the first, third and fifth sections are mainly plagiogranite and Yangqi chlorite plagioclase schist, The second and fourth rocks are the combination of the Changling schist and metamorphic rhyolite. The original rock in the Bai Nai Miao Formation is a suite of medium- to medium-acid marine volcano-sedimentary rocks. For the deposit and the formation of the Bai Nai Miao formation strata disputes, the predecessors many believe that both were formed in the Mesoproterozoic. In this paper, the formation age of the third lithologic greenschist plagioclase schist in the Baimiao Miao Formation is 439.8 ± 6.7Ma and the age of formation of granodiorite porphyry is 433.9 ± 2.2Ma using zircon SHRIMP U-Pb isotopic dating. 451.8 ± 3.0Ma. The molybdenite formation age was 433.9 ± 3.1Ma by the molybdenite Re-Os isotope analysis. Combined with the previous achievements, it is proposed that the diagenetic age of the Bai Nimiao Formation and the granodiorite porphyry and the mineralization age of the Bai Nai Miao copper deposit are both Late Ordovician-Early Silurian, both of which belonged to the Paleozoic Baimai Island Arc Magma products.