东昆仑夏日哈木铜镍矿床Ⅱ号岩体年代学、地球化学及其意义

摘要

夏日哈木超大型镍矿床位于东昆仑造山带昆中岛弧带内,其Ⅱ号岩体主要由辉长岩和少量辉石岩组成,局部可见孔雀石、镍华、褐铁矿、磁黄铁矿、镍黄铁矿、黄铜矿等矿化.岩石主量元素化学特征具低硅(w(SiO2)=48.12％～50.18％)、低钛(w(TiO2)=0.47％ ～0.73％)、高镁(w(MgO)=13.15％ ～19.59％)的特征,属亚碱性系列岩石,m/f值为3.14～3.88,属铁质超基性岩类.岩石稀土、微量元素标准化配分模式具一致性,表现为轻稀土元素弱富集的右倾型,并具有富集大离子亲石元素,亏损高场强元素Nb、Ta、Ti的特征.辉长岩的锆石SHRIMP U-Pb年代学研究表明,岩体形成年龄为(424.1±4.6) Ma,属志留纪.笔者对夏日哈木Ⅰ号、Ⅱ号岩体的主要地质特征作了对比,认为二者同源,结合区域构造及Ⅰ号岩体形成的构造背景,认为Ⅱ号岩体形成于岛弧环境.%The Xiarihamu super large nickel deposit is located in the island arc zone in the middle part of the western segment of the East Kunlun orogenic belt.The No.Ⅱ intrusion is mainly composed of gabbro and pyroxenite with mineralization such as limonite,pyrrhotite,pentlandite and chalcopyrite.Major element values of Xiarihamu No.Ⅱ intrusion show sub-alkalic series and are characterized by low SiO2 content (48.12％～50.18％)and low TiO2 content (0.47％ ～0.73％),but high MgO content (13.15％ ～19.59％).The m/f ratios of the rocks range from 3.14 to 3.88,falling into the range of ferrous-ultramafic rocks.LREE-rich trace elements patterns are enriched in LILE and relatively depleted in HFSE (Nb,Ta,Ti).Zircon SHRIMP U-Pb dating of gabbro yielded (424.1 ± 4.6) Ma,suggesting it formed in Silurian.In this paper,the geological characteristics between Xiarihamu No.I and No.[Ⅱ intrusions were compared,which shows the same comagmatic evolution for No.Ⅰ and No.Ⅱ intrusions.Combined with regional tectonic evolution and structural setting of No.Ⅰ in-trusion,the authors conclude that No.Ⅱ intrusion was formed in an island arc setting.