东天山西凤山金矿花岗岩锆石U-Pb年龄、地球化学及其对成岩成矿时代的限定

Zircon U-Pb geochronology and petrogeochemistry of granitic rocks of the Xifengshan gold deposit in eastern Tianshan and limitation on diagenesis and mineralization times

为探讨西凤山金矿岩浆活动与成矿作用关系,对赋矿花岗岩类岩体(脉)(花岗岩、花岗斑岩、石英斑岩)分别进行了LA-ICP-MS锆石U-Pb同位素定年,获得加权平均年龄为(329.5±4.3) Ma、(324.6±4.6) Ma和(320.0±4.0) Ma,成岩时代为晚石炭世。地球化学表明,花岗岩具有富硅、略富铝,富钠低钾特征,属于钙碱性-高钾钙碱性、过铝质系列,具有Ⅰ型花岗岩特征。稀土元素配分曲线为平缓型,轻重稀土元素分馏明显,负Eu异常,微量元素富集Rb、Th和K,亏损Nb、Sr、P。综上所述,岩体形成于哈萨克斯坦-准噶尔板块与塔里木板块碰撞造山环境,成岩时代(329~320 Ma)早于成矿时代(272 Ma);相应成矿作用与康古尔韧性变形带的变形过程相耦合,具有韧性剪切带型金矿的特点。

In order to explore the coupling relationship between magmatism and mineralization of the Xifengshan gold deposit,LA-ICP-MS zircon U-Pb isotopic dating has been carried out for the ore bearing granitic rocks(veins)( granite,granite porphyry and quartz porphyry) in this paper,gives respectively a weighted average age of 329.5±4.3 Ma、324.6±4.6 Ma和320.0±4.0 Ma,indicating that the granites intruded in the Late Carboniferous Epoch. Geochemically,the granites are characterized by high contents of Si,Al,Na and low K,belong to series of high-K-calc-alkaline and peraluminous,which belonges to Ⅰ type granite.Their REE and trace elements are enriched in LREE,Rb,Th and K,and differently depleted in Sr,Nb,P and Ti,with strong negative anomalies of Eu. The study shows that the granites( veins) formed in the compressional tectonic setting of the collisional orogeny between the Kazakhstan Junggar plate and the Tarim plat;The diagenetic age(329-320 Ma) is obviously early the metallogenic age(272 Ma),and is coupled with the deformation process of the Kangur ductile deformation zone.Therefore,it is considered that the deposit has the characteristics of ductile shear zone type gold deposits.