辽宁鞍本地区铁矿床黄铁矿和辉钼矿Re-Os同位素测年及其地质意义

Re-Os isotopic dating of pyrite and molybdenite from the iron deposits in Anshan-Benxi area of Liaoning Province and its geological significances

本文利用Re-Os同位素体系(ICP-MS方法)对1件辉钼矿和10件黄铁矿样品进行定年。1件辉钼矿的ReOs模式年龄为(2376±37)Ma,10件黄铁矿获得了3组Re-Os年龄:1(2567±36)Ma^(2540±37)Ma(模式年龄);2(2237±112)Ma(模式年龄);3(1572±140)Ma(等时线年龄)。(2376±37)Ma的辉钼矿形成于古元古代,是目前中国已知最老的辉钼矿年龄之一,其成矿物质来自地壳,(2237±112)Ma的黄铁矿属于热液成因,其成矿物质来自地壳,(2376±37)Ma^(2237±112)Ma的Re-Os年龄代表了一次重要的热液改造事件;(2567±36)Ma^(2540±37)Ma的黄铁矿是原始沉积形成的,是目前中国已知最老的黄铁矿年龄,该年龄代表了2.5Ga形成BIF的地质事件;(1572±140)Ma的黄铁矿形成于中元古代,具有明显的壳源特征,该年龄代表了一次较晚期的热液改造事件。这些年龄为确定鞍本地区铁矿的热液活动时间提供了新的重要证据,对深入认识区域成矿规律和探讨地质构造演化具有重要意义。

Rhenium and osmium isotopes in a molybdenite sample and ten pyrite samples were used to determine the timing of mineralization by ICP-MS. Re-Os model age of the molybdenite sample is （2376±37）Ma, Re-Os ages of the ten pyrite samples yielded three kinds of ages ： （1） （2567±36）Ma-（2540±37）Ma （model age）; （2） （2237±112）Ma （model dating）; （3） （1572±140）Ma （isochron age）. These data suggest that the molybdenite of（2376±37）Ma was formed during early Proterozoic, and was the oldest Re-Os model age of molybdenite, the pyrite of（2237± 112）Ma was formed during early Proterozoic, and both of them indicate that the molybdenite and the pyrite were derived from the crust and represented an important hydrothermal activity in 2.3 Ga; the pyrite of （2567±36）Ma-（2540±37）Ma was formed during new Archaeozoic period and yielded the oldest Re-Os model age, which indicates that the pyrite was formed with BIF in 2.5 Ga; the pyrite of（ 1572± 140）Ma was formed during middle Proterozoic, which indicates that pyrite was derived from the crust and represented a hydrothermal activity. The Re-Os isotopic dating result provides a new proof for the existence of hydrothermal activity in iron deposits of the Anshan- Benxi area, and is also important for understanding the ore-forming processes and tectonic evolution in this area.