胶东祥山铁矿的成因探讨:来自铁矿石和宿主岩的岩石学、矿物化学和年代学证据  

Genesis of the Xiangshan iron deposit in Jiaodong:Petrography and mineral chemistry evidence from iron ore and host rocks

作　　者：李旭平 陈燕平 李增胜 李洪奎 陈莉 陈妍蓉 孔凡梅 LI XuPing;CHEN YanPing;LI ZengSheng;LI HongKui;CHEN Li;CHEN YanRong;KONG FanMei(Shandong Provincial Key Laboratory of Depositional Mineralization and Sedimentary Minerals,College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao 266510,China;Shandong Institute of Geological Sciences,Jinan 250013,China)

机构地区：[1]山东省沉积成矿作用实验室,山东科技大学地球科学与工程学院,青岛266510 [2]山东省地质科学研究院,济南250013

出　　处：《岩石学报》2022年第10期3209-3230,共22页Acta Petrologica Sinica

基　　金：国家自然科学基金委山东联合基金重点项目(U1906207)资助。

摘　　要：祥山富磷灰石铁矿出露在烟台莱山地区,位于胶-辽-吉造山带中的胶东半岛,也是我国重要的胶东金矿成矿区。矿体赋存在胶北地体的前寒武系荆山群中,原岩为侵入到表壳岩中的层状镁铁-超镁铁质岩体。铁矿石呈块状和致密浸染状,以透镜体和脉体形式产出在岩体中,且与岩体走向一致。矿体和宿主岩均经历了角闪岩相变质作用。宿主岩地球化学研究显示其形成于与岛弧相关的陆内造山环境。宿主岩和铁矿石的锆石U-Pb年龄分别为1889Ma和1832~1841Ma的变质年龄,分别代表了胶-辽-吉造山带碰撞、折返的年龄,也代表了铁矿石最早形成年龄的上限。铁矿石中磷灰石有两期,早期磷灰石(Ap-Ⅰ)与宿主岩的磷灰石都具有轻稀土富集的岩浆成因特征,而晚期磷灰石(Ap-Ⅱ)呈现中稀土凸起的变质成因特征。宿主辉石角闪岩、铁矿石早期磷灰石和晚期磷灰石的U-Pb年龄分别为131±17Ma、368±36Ma和285±22Ma。对应于磷灰石,铁矿石中的磁铁矿也有两期,V、Ti、Cr、Fe、Ni等亲铁元素同样表现出早期磁铁矿(Mag-A)与宿主岩的磁铁矿都具有岩浆成因特征,而晚期磁铁矿(Mag-B)呈变质成因。但铁矿石中的早期磁铁矿(Mag-A)与宿主岩的磁铁矿均受到了晚期热液作用的影响而发生了再平衡过程,可能是在早期磷灰石形成时(~368Ma)的重结晶过程中发生了微量元素的再平衡作用。磷灰石的~285Ma年龄代表了铁矿石的最后一期成矿时间,而宿主岩中磷灰石记录的~131Ma的年龄与胶东金成矿期年龄一致,是与研究区铁成矿无关的一次热液交代事件。鉴于铁矿石中磷灰石与磁铁矿的结构关系,本文认为祥山磁铁矿的成矿作用形成于中元古代胶辽吉造山带的折返过程,后期叠加了晚泥盆和早二叠世的热液富集成矿。磁铁矿的主微量元素研究表明,祥山铁矿的成因是岩浆-热液混合成因,具有Kiruna型铁矿特征。Xiangshan apatite-rich iron ore deposit is located in jiaodong Peninsula of the jiao-Liao-Ji orogenic belt,and it is also an important jiaodong gold mining area in China.The ore body occurs in the Precambrian Jingshan Group of Jiabei terrane,and the protolith is mafic-ultramafic intrusions in the supracrustal sequence.Iron ore occurred in the host rock is in the form of lenticular and banded ore body with massive,densely disseminated texture,which is consistent with the strike of host rock.Both ore body and host rock underwent amphibolite facies metamorphism.The host rock geochemistry of the Xiangshan iron deposit shows that it was formed in an arc affinitive intracontinental orogenic environment.Zircon U-Pb ages of host rock and iron ore are 1889 Ma and 1832~1841 Ma,respectively,which represent the ages of Jiao-Liao-Ji orogenic belt collision and exhumation,respectively.Zircon ages from iron ore also represent the age of the earliest stage of iron ore formation.There are two stages of apatite formation in iron ore.The early apatite(Ap-Ⅰ)and the apatite of host rock are magmatic origin with enrichment in LREE,while the late apatite(Ap-Ⅱ)is metamorphic with MREE protrusion.The apatite U-Pb ages of the host pyroxene amphibolite,early apatite(Ap-Ⅰ)and late apatite(Ap-Ⅱ)are 131±17 Ma,368±36 Ma and 285±22 Ma,respectively.Corresponding to apatite,magnetite in iron ore also has two stages.The characteristics of V,Ti,Cr,Fe,Ni and other ferrophilic elements show that the magnetite in the early Mag-A and the magnetite in the host rock are of magmatic origin,while the magnetite in the late Mag-B is of metamorphic origin.However,the magnetite in the early Mag-A and the magnetite in the host rock were both affected by the hydrothermal process,which may be attributed to the rebalancing of trace elements during the recrystallization of the early apatite formation at~368 Ma.The~285 Ma age of apatite represents the last mineralization of iron ore,while the~131 Ma age of apatite in host rock is consistent with the age o

关 键 词：祥山铁矿 锆石U-PB定年 磷灰石U-Pb定年 磁铁矿微量元素 铁矿成因 

分 类 号：P588.124[天文地球—岩石学] P588.125[天文地球—地质学] P618.31