摘要
鉴于缺少可直接用于同位素测年的金属矿物,许多钨矿床的成矿时代大多数是悬而未决的地质难题。本文以我国著名北京密云沙厂环斑花岗质杂岩体内产出的黑钨矿为研究对象,对钨矿床的形成年龄进行了测定,8件黑钨矿Sm-Nd同位素等时线年龄为1430±93Ma(2σ),Nd初始比值为0.510992±3(2σ)和ε_(Nd)(1430Ma)为-10.5±0.84(2σ),这是迄今在我国测定到的最老的钨矿床成矿年龄。通过对全国已有钨矿床同位素年龄数据的对比分析,并且结合它们的地质与地球化学特征,可以认为,我国最古老的钨矿床很可能形成于中元古代,而并非是古生代。另外,密云沙厂地区钨矿床的成矿作用与中元古代富矿碱性岩浆活动有关。
This paper presents Sm-Nd isotope data for Archean metamorphic gneiss and Mesoproterozoic rapakivi granitoid samples as well as wolframite separates from the Shachang district, Miyun County, Beijing, China. Eight wolframite separates occurring within the Shachang rapakivi granitoid intrusive complex give a Sm-Nd isochron age of 1430 ± 93 Ma (2σ) and εNd(1430 Ma) value of -10. 5 ± 0. 84 (2σ). This age may represent the precipitation time of the wolframite at Shachang, and has been considered as the oldest age of tungsten mineralizatiion in China. Moreover, Nd isotopic data of the Archean gneiss, Mesoproterozoic rapakivi granitoid intrusive complex and their associated wolframites suggest that the tungsten-bearing quartz veins at Shachang are derived from mixed sources of the depleted mantle and upper crust. The tungsten mineralization occurring within the Shachang rapakivi granitoid intrusive complex is spatially and temporally associated with Proterozoic alkaline magmatism.
出处
《地质论评》
CAS
CSCD
北大核心
2002年第1期29-33,共5页
Geological Review
基金
国家重点基础研究项目(编号G1999043207-4)
国家自然科学基金项目(编号40073015)
