摘要
首次采用SHRIMP锆石微区U—Pb测年技术，对雷门沟花岗斑岩体进行年代学研究，通过对花岗斑岩中单颗粒锆石25个样品点的分析，获得了两组年龄数据，其中有11个分析点形成谐和年龄，其^206Pb／^238U年龄范围在129．1±3．0～138．4±2．3Ma之间，加权平均值为136．2±1．5Ma；另外9个分析点的^207Pb／^206Pb年龄集中于1884±20～2629±7Ma；前者指示了雷门沟岩体的结晶年龄为侏罗纪白垩纪之交。后者则代表了岩体侵位过程中捕获的太华群错石的年龄。首次采用ICPMS法测定雷门沟斑岩型钼矿中的辉钼矿Re-Os同位素年龄，获得其模式年龄为131．6±2．0～133．1±1．9Ma,加权平均值为132．4±1．9Ma，指示了雷门沟钼矿床的成矿年龄。两种精测方法获得的年龄相吻合，成岩与成矿大致同时或成矿略晚于成岩。测试结果表明雷门沟斑岩钼矿与金堆城等东秦岭钼矿带其他钼矿床基本同时形成。
Located on the eastern portion of the East Qinling Molybdenum Belt, the Leimengou deposit is a large porphyry Mo deposit. This study provides the first high-precision dating of the mineralization and rock-forming in the Leimengou Mo deposit. The zircon SHRIMP dating of the Leimengou granitic porphyry gave two groups of ages, in which eleven analyses presented ^206Pb/^238U concordant ages from 129.1±3.0Ma to 138.4±2.3Ma with a weighted mean age at 136.2±1.5Ma, and other nine analyses provided ^207Pb/^206Pb ages from 1884 Ma to 2629 Ma. The former indicates that the crystallization of the Leimengou granitic porphyry occurred at the Jurassic-Cretaceous turn, and the latter is interpreted as the age of inherited magmatic zircon in the Taihua Group. Meanwhile, the ^187Re and ^187Os contents of molybdenite from the molybdenum deposit are determined by Inductively Coupled Plasma Mass Sperctrometry （ICP-MS）, with analytical errors of Re and Os between 0. 2%-0. 3% （20）. The results show that the Re-Os model ages of the deposit are between 133.1±1.9-131. 6±2.0 Ma , averaging 132.4±2.0Ma , which accurately determines the timing of mineralization. The zircon SHRIMP U-Pb and molybdenite Re-Os isotopic dating are quite close, which indicate that the mineralization developed almost simultaneously with or slightly later than the emplacement of the granite stock. We suggest that the Leimengou Mo deposit was formed at about the same time as the Jinduicheng deposit and other molybdenum deposits in the East Qinling molybdenum belt.
出处
《地质论评》
CAS
CSCD
北大核心
2006年第1期122-131,共10页
Geological Review
基金
国家自然科学基金重点项目(编号40434011)
国家重点基础研究发展规划项目(编号G1999043211)的成果
