西藏班戈地区重要矽卡岩型铁（铜）多金属矿床LA-ICP-MS锆石U-Pb测年与花岗岩地球化学特征

选择班戈县雪如、查朗拉2个重要的小型矽卡岩型铁铜矿床为研究对象,在系统的野外地质调查、样品采集和室内岩矿鉴定、分析测试工作的的基础上,开展了2个矿床LA-ICP-MS锆石U-Pb测年与花岗岩地球化学研究。LA-ICP-MS方法测定的锆石U-Pb年龄显示,雪如、查朗拉地区成矿岩体年龄分别为79.72Ma±0.50Ma和76.10Ma±0.40Ma,证明班戈地区存在晚白垩世的岩浆活动。2个岩体的SiO2含量介于70.45%～72.64%之间,K2O（4.62%～5.69%）的含量均高于Na2O（3.05%～3.75%）的含量,CaO的含量偏低（1.32%～2.03%）,富K。A/CNK均小于1.0,A/NK范围为1.03～1.30,为准铝质类型。显示富K特征。在微量元素蛛网图中,富集大离子亲石元素Ra、Th、U、Nd,贫Nb。稀土元素配分模式属于右倾型,∑REE=199.08×10-6～268.41×10-6,LREE/HREE=4.71～7.68,具有中等的负Eu异常。岩体为同碰撞期花岗岩类,具有良好的铁铜铟铋等多金属成矿地质、地球化学条件,显示有良好的找矿前景。

LA-ICP-MS zircon U-Pb dating of important skarn type iron（copper） polymetallic deposits in Baingoin County of Tibet and geochemical characteristics of granites

With two important small skarn type iron（copper） deposits（Xueru and Chalangla） as the study objects,the authors made detailed field geological survey,collected samples and performed indoor rock appraisal,zircon LA-ICP-MS U-Pb dating and analysis of major and trace elements.The zircon LA-ICP-MS dating results of the metallogenic rocks are 79.72Ma±0.50Ma and 76.10Ma±0.40Ma,suggesting that late Cretaceous magmatism existed in Baingoin area.The contents of SiO2 are in the range of 70.45%～72.64%,the contents of K2O（4.62%～5.69%） are higher than that of Na2O（3.05%～3.75%）,the contents of CaO（1.32%～2.03%） are somewhat lower,and the rock samples are rich in potassium.A/CNK ratios are lower than 1.The rocks belong to metaluminous series with A/NK ratios being 1.03～1.30.The rocks are characterized by high potassium.In the spider diagrams of rare elements,they are enriched in large ion lithophile elements such as Ra,Th,U and Nd and depleted in Nb.REE distribution curve is significantly rightly oblique.REE values range from 199.08×10-6 to 268.41×10-6,LREE/ HREE ratios range from 12.13 to 19.27 with medium negative Eu anomalies.The granites were formed in the same syn-environment and possessed favorable geological and geochemical conditions for iron copper polymetallic mineralization.Thus ore prospecting in this area is promising.