华北地台钼（铜）矿床成矿年代学研究——辉钼矿铼－锇年龄及其地质意义

METALLOCHRONOLOGY OF MOLYBDENUM ( COPPER) DEPOSITS IN THE NORTH CHINA PLATFORM:Re Os AGE OF MOLYBDENITE AND ITS GEOLOGICAL SIGNIFICANCE

华北地台北缘的燕辽和南缘的东秦岭两个钼矿带闻名遐迩。本文用同位素稀释－等离子体质谱法，直接测定了燕辽钼矿带中兰家沟钼矿床的Ｒｅ－Ｏｓ等时线年龄为（１８６．５±０．７）×１０６ａ，杨家杖子和肖家营子钼矿床的Ｒｅ－Ｏｓ模式年龄为（１８７±２）×１０６～（１９１±６）×１０６ａ和（１７７±５）×１０６ａ，小寺沟和寿王坟铜（钼）矿床的Ｒｅ－Ｏｓ模式年龄为（１３４±３）×１０６ａ和（１４８±４）×１０６ａ，大湾和大庄科钼矿床的Ｒｅ－Ｏｓ模式年龄为（１４４．４±７．４）×１０６ａ和（１４４．７±１０．７）×１０６～（１４７．１±６．６）×１０６ａ。结合东秦岭钼矿带内钼矿床的Ｒｅ－Ｏｓ年龄，证明华北地台内有早元古代钼矿化，两个钼矿带中的钼或铜（钼）矿床的成矿时代主要为印支期和燕山早期或中—晚期。Ｒｅ－Ｏｓ法不仅是直接测定钼（铜）硫化物矿床成矿年龄的一种新手段，而且所获结果为研究区域成矿演化提供了确实的依据。

The North China platform is the most important molybdenum metallogenic province of China, which consists of the Yanliao molybdenum ore belt on the northern margin and the East Qinling molybdenum ore belt on the southern margin. The two molybdenum ore belts are controlled by the Mesozoic tectonic magmatic belts in the Yanshan platform fold belt and the Henan Shaanxi uplifting area as well as their molybdenum geochemical anomalous fields. Molybdenum ( copper) sulfide deposits had been traditionally dated by indirect methods such as K Ar or Rb dating techniques, in which ages were determined by measuring isotopes of intrusive rocks related to mineralization, minerals from altered wall rocks, and gangue minerals from orebodies. In our study, ID ICP MS technique was used, which directly determined Re Os ages of molybdenites from molybdenum or copper molybdenum deposits. The results obtained show that (1) the Tongkuanyu metaporphyry type copper molybdenum deposit(with the Re Os isochron age of 2108×10 6 a) and the Bizigou sedimentary metamorphic copper molybdenum deposit (with the Re Os model ages of 1919×10 6～1980×10 6 a) in the Shanxi platform uplift wre formed respectively in early period and late period of Early Proterozoic;(2) Mineralization of molybdenum or copper molybdenum deposits in the Yanliao molybdenum ore belt took place in early Yanshanian period (the Re Os isochron age of the Lanjiagou porphyry molybdenum deposit is 185.5×10 6 a, the Re Os model model ages of the Yangjiazhangzik and Xiaojiayingzi skarn type molybdenum deposits are 187×10 6～191×10 6 a and 177×10 6 a, respectively) and middle late Yanshanian periods (the Re Os model age of the Dazhuangke explosive breccia type molybdenum deposit is 144.4×10 6 a, the Re Os mo del ages of the Xiaosigou and Shouwangfen porphyry skarn type copper molybdenum deposits are 134×10 6a and 148×10 6a, respectively). The mineralization ages of molybdenum deposits in the East Qinling molybdenum deposits are dominantly Indosinian (the Re Os isochron age of the Huanglongpu carbonatite vein type molybdenum (lead) deposit is 221×10 6 a) and middle late Yanshanian (the Re Os isochron age of the Nannihu Sandaozhuang porphyry skarn molybdenum tungsten deposit is 147×10 6a, the Re Os model ages of the Jinduicheng and Shijiawan porphyry molybdenum deposits are 129×10 6～139×10 6 a and 138×10 6 a, respectively). Despite the existence of the early Proterozoic molybdenum mineralization in the North China platform, the molybdenum ore deposits of the Yanshanian or Indosinian period are of the highest economic value. The above results provide valuable Re Os ages for the understanding of the evolution of molybdenum or copper molybdenum mineralization in the North China platform.