黑龙江三道湾子金矿床火山岩-次火山岩年代学、地球化学和地质意义

摘要

三道湾子金矿床位于小兴安岭北麓,是典型的以碲金化合物为主的矿床,为了限定其成矿时代和厘定其成矿地质背景,笔者对同成矿地质体火山岩和成矿期后的玄武粗安玢岩的单颗粒锆石U-Pb年龄和元素地球化学进行测定,获得同成矿地质体粗面英安斑岩及玄武粗安玢岩的206Pb/238U年龄加权平均值分别为(124.2±0.9)Ma(MSWD=0.5,n=18)和(118.9±2.3)Ma(MSWD=0.5,n=6);赋矿围岩为玄武粗安岩与同成矿地质体粗面英安斑岩,SiO2含量为52.75％～62.30％,K2O和Na2O含量分别为2.02％～2.85％和3.96％～4.24％.里特曼指数(δ)在0.85～3.67之间,属于钙碱性到高钾钙碱性岩系特征;成矿期后脉岩玄武粗安玢岩,SiO2含量为51.53％～52.32％,K2O含量为2.30％～2.36％,Na2O含量为3.78％～4.14％,里特曼指数(δ)在4.05～4.86之间;微量和稀土元素均显示富集大离子亲石元素(Cs、K、Rb、Ba、LREE等),相对亏损高场强元素(Nb、Ta、Zr、Hf等)和HREE,特别是强烈亏损Th、U和Nb、Ta的特征,与岛弧钙碱性玄武岩相似.研究揭示了该矿床形成于早白垩世(124～119 Ma)或晚中生代造山后伸展构造环境,成矿热动源可能是交代大洋性质的岩石圈地幔.%Sandaowanzi gold deposit is a typical gold telluride minerals deposit,located at the northern edge of the Xiao Xing`an range,NE China.In order to reveal the ore-forming geological setting,the authors recently conducted studies on geochronology and geochemistry of volcanic rocks hosting the deposit.The results show that the zircon U-Pb ages of the trachydacite porphyry from the syn ore-forming geological bady and basaltic trachyandesite porphyry from ore-forming rock are(124.2±0.9)Ma(MSWD=0.5,n=18)and(118.9±2.3)Ma(MSWD=0.5,n=6); Volcanic rocks from the basaltic trachyandesite and trachydacite porphyry are high in SiO2(52.75％～62.30％),and the K2O and Na2O are 2.02％～2.85％and 3.96％～4.24％,respectively; Rittman index(δ)is between 0.85 and 3.67,which belongs to the high-K calc-alkaline to calc-alkaline series; the dike of basaltic trachyandesite porphyry formed after mineralization is with SiO2 of 51.53％～52.32％,K2O of 2.30％～2.36％,Na2O of 3.78％～4.14％,and Rittman index(δ)is between 4.05 and 4.86; these rocks are characterized by enrichment in large ion lithophile elements(LILEs,such as Cs,K,Rb,Ba,and LREEs)and depletion in high field strength elements(HFSEs,such as Nb,Ta,Zr,Hf,and HREEs),especially the features of strong positive Th,U,Nb,and Ta,which is similar to the calc-alkaline island arc basalt.It is concluded that the Sandaowanzi gold deposit formed in the Early Cretaceous(124～119 Ma)or Late Mesozoic post-collision extensional setting.The source may be the oceanic lithosphere mantle,which was mixed with crustal material in magma evolution,and the mineralization is closely related to the Early Cretaceous subalkalic volcanic-rocks.