北山造山带花牛山岛弧东段钨矿床成矿时代和成矿动力学过程

北山造山带位于中亚造山带最南缘,为多期岛弧、蛇绿混杂岩拼贴而成的增生型造山带;晚古生代,北山造山带的构造活动引发强烈的花岗质岩浆活动,伴随有广泛的钨(钼)成矿作用;本文对北山南带花牛山岛弧三个典型含钨花岗岩体:盘陀山、鹰嘴红山及玉山岩体进行详细的锆石U-Pb年代学、全岩地球化学研究。SIMS锆石U-Pb定年结果表明该区成矿花岗岩分为两个侵入期次:(1)晚志留世月牙山-洗肠井蛇绿混杂岩南段出露花岗岩,其中,盘陀山二长花岗岩422.0±1.5Ma;盘陀山钾长花岗岩417.0±1.7Ma;鹰咀红山钾长花岗岩424.0±1.3Ma;(2)晚二叠世柳园蛇绿混杂带北侧玉山花岗岩体,定年结果为280.8±3.0Ma。岩石地球化学研究表明盘陀山-鹰嘴红山花岗岩带为过铝质S型花岗岩,玉山岩体为A型花岗岩。岩体稀土含量较高,具右倾型稀土配分模式,LREE分异强烈,HREE分异不明显,样品Eu亏损强烈。原始地幔标准化蛛网图中总体显示较为一致的分布模式,大离子亲石元素Ba、Sr呈现明显负异常,富集Th、U、Pb、Zr、Hf等元素而亏损高场强元素Ta、Nb、Ti、P。结合晚古生代北山构造演化过程,推断国庆-鹰嘴红山钨矿为公婆泉岛弧与花牛山岛弧碰撞阶段形成,而玉山钨矿床为晚华力西期弧后伸展构造背景的产物。

Geochemistry and U-Pb geochronology of tungsten deposit of Huaniushan island arc in the Beishan Orogenic Belt, and its geodynamic background

The newly-discovered tungsten deposits are located in the Beishan Orogenic Belt, NW-China, Central Asian Orogenic Belt. There are three mineralized granitoid intrusives of them: the Pantuoshan, Yingzuihongshan and Yushan. By high-precision SIMS zircon U-Pb dating, we obtained the concordant age of 422.0±1.5Ma and 417.0±1.7Ma for monzogranite and K-feldspar granite of Pantuoshan ore-bearing intrusion, and K-feldspar granite of Yingzuihongshan emplaced at age of 424.0±1.3Ma. In addition, we have got the age of 280.8±3.0Ma of Yushan granite. The geochemical data shows that the three intrusions characterized by high REE and LREE-rich pattern, enriched LILE (Th, Zr, Hf) and HFSE (U, Pb), depleted HFSE (Ta, Nb, Ti, P). In combination with the evolution of the Paleozoic Beishan Orogenic Belt, we suggest that the Guoqing and Yingzuihongshan tungsten deposits occurred by the collision between Gongpoquan and Huaniushan island arc, and Yushan tungsten deposit formed in the Late Paleozoic back-arc extension tectonic setting.