新疆东天山小白石头钨(钼)矿辉钼矿Re-Os同位素年龄及成矿时代

Re-Os Isotopic Age of Molybdenite from the Xiaobaishi W-(Mo) Deposit,Eastern Tianshan,Xinjiang and Its Geological Implication

小白石头钨(钼)矿床位于新疆东天山造山带中的中天山地块南缘,该矿床是一个由黑云母花岗岩和花岗闪长岩侵入中元古界卡瓦布拉格群形成的矽卡岩型钨(钼)矿床。辉钼矿作为其主要的矿石矿物之一,呈不同产出状态分布于花岗闪长岩、黑云母花岗岩、矽卡岩和石英脉中。目前,对于小白石头钨(钼)矿成矿时代尚有争议,特别是与花岗闪长岩有关的辉钼矿化形成时代缺乏精确的限定。本文选取与花岗闪长岩有关的不同产状辉钼矿进行Re-Os同位素定年,获得Re-Os加权平均模式年龄为245. 0±1. 7Ma,Re-Os等时线年龄为245. 5±4. 3Ma。准确的Re-Os同位素定年限定小白石头钨(钼)矿床的成矿年龄和花岗闪长岩的侵位年龄为245Ma左右,为矿床模型建立和找矿方向确定提供了关键依据,同时也为东天山区域成矿规律总结提供了重要的年代学证据,并指出新疆东天山—甘肃北山地区存在一条找矿潜力巨大的三叠纪钨钼成矿带。

BACKGROUND:The Xiaobaishitou W-(Mo)deposit is located in the Central Tianshan Massif of the Eastern Tianshan,Northwestern China.The deposit is a skarn-type tungsten-molybdenum deposit formed by biotite granite and granodiorite intruding into the Mesoproterozoic Kawabulag Group.As one of the most important ore minerals,molybdenite is distributed in granodiorite,biotite granite,skarn and quartz veins.OBJECTIVES:To use molybdenite in order to constrain the mineralization age of the Xiaobaishitou W-(Mo)deposit by Re-Os dating.METHODS:Different molybdenite grains associated with the granodiorite from the Xiaobaishitou W-(Mo)deposit were selected for Re-Os isotopic dating.The results were compared with the Xiaobaishitou biotite granite age and the chronological data of other Triassic tungsten-molybdenum deposits in the Eastern Tianshan.RESULTS:The molybdenite Re-Os weighted average model age and Re-Os isochron age are 245.0±1.7Ma and 245.5±4.3Ma,respectively.CONCLUSIONS:The dating results indicate that the molybdenite age for mineralization and the emplacement age of the granodiorite are around 245Ma,which is similar to the age of the Xiaobaishitou biotite granite.It provides a key basis for the establishment of an ore deposit model and the determination of the direction for ore prospecting.It also provides important chronological evidence for the ore-forming laws in the eastern Tianshan,and points out that there is a great prospecting potential for a Triassic tungsten and molybdenum metallogenic belt in the eastern Tianshan-Beishan of Gansu.