桂北油麻岭钨矿区成矿岩体的年代学、地球化学及其地质意义

摘要

油麻岭钨矿位于桂北苗儿山复式岩体最南缘,矿化类型具有多样性,其中外接触带似层状矽卡岩型白钨矿是矿区最重要的矿床类型.本文对矿区成矿母岩中-细粒二云母花岗岩进行了锆石U-Pb年代学和岩石地球化学的研究.LA-ICP-MS锆石U-Pb年龄为212~215 Ma,属印支期岩浆活动的产物.地球化学分析显示,花岗岩具有高硅(SiO2=73.73%~78.68%)、富碱(ALK=6.99%~8.36%)、贫Ca(CaO=0.13%~0.96%)、贫Ti(TiO2=0.05%~0.27%)、弱过铝-强过铝质(ACNK=1.03~1.28)的特征,稀土元素总量偏低(∑REE=61.39×10-6~161.22×10-6),富集Rb和Cs大离子亲石元素及Th,U,Ta等高场强元素,富成矿元素W (平均含量6.55×10-6),贫Ba和Sr,强烈的Eu亏损(δEu=0.04~0.20).岩石学和地球化学特征表明,成矿母岩与南岭地区典型的高分异S型花岗岩相似.该岩体具备为钨矿的形成提供物源的能力.%Youmaling tungsten deposit is located in the southern margin of the Miaoershan granitic complex in the northern Guangxi province. Its mineralization types are diverse, and the main type is stratoid skarn-type scheelite in outer contact zone of the granite body. In this study, we carried out a comprehensive research including zircon U-Pb dating,petrology and geochemical studies on the granite related to the tungsten deposit. Petrologically,it is medium-fine grained two-mica granite. LA-ICP-MS zircon U-Pb chronology indicates that the granitic pluton emplaced at 212~215 Ma during the Indosinian period. Chemical analyses show that the granite has high SiO2(SiO2=73.73%~78.68%),high alkalies(ALK=6.99%~8.36 %),low Ca and Ti (CaO=0.13%~0.96%,TiO2=0.05%~0.27%),and is slightly-strongly peraluminous(ACNK=1.03 ~1.28);The granite also displays low total REE contents(∑REE=61.39×10-6~161.22×10-6),with strong negative Eu anomalies(δEu=0.04~0.20), and is enriched in Rb,Cs etc. LILEs,Th,U,Ta etc. HFSEs and ore-forming element W(averaging 6.55ppm),depleted in Ba, Sr. These characteristics are similar to the typical highly fractionated S-type granites in Nanling region. Our petrological and geochemical data suggest that the granite has the ability to provide materials for formation of tungsten deposit.