西秦岭阳山超大型金矿床花岗岩岩石地球化学特征

阳山超大型金矿床是中国乃至亚洲发现的首个金资源量超过300 t的矿床,该矿床的形成与矿区花岗岩脉关系密切。从阳山花岗岩的地球化学特征入手,探讨出露的斜长花岗斑岩和花岗细晶岩的特征。阳山花岗岩为钙碱性系列,属强过铝质,分异指数(DI)(71.12～87.0)较高,表明原始岩浆分异强烈;稀土元素配分图为右倾型,∑REE较低(32.18×10-6～100.21×10-6,)LREE/HREE大多数在7以上;高场强元素(Nb、Ta、Zr)为负异常,Rb/Sr为0.38～2.08,阳山花岗岩在构造环境判别图上为碰撞后环境。2种花岗岩为同一来源,只是形成的时间有差别。结合区域地质特征和前人的年龄数据,得出阳山超大型金矿形成于华北与扬子陆块碰撞后的拉张环境。

Petrology and Geochemistry of Granites in Yangshan Ultra-large Gold Deposit, West Qinling

Yangshan ultra-large gold deposit is the first discoveried deposit of more than 300 tons of gold resource in China and even whole Asia.The relationship of the deposit and the granites in orefield is very close.We discuss the characters of plagioclase granite porphyry and granite aplite esposed in Yangshan area from the start of geochemistry characters of granites in Yangshan deposit.Yangshan granites belongs to calc-alkali magma series and superperaluminous.The higher differentiation index（71.12～87.0） indicates the intense differentiation of origin magma.The partion chart of rare earth elements is right deviation,lower ∑REE（32.18×10-6～100.21×10-6）,the major of LREE/HREE upwards seven.High field strong elements（Nb、Ta、Zr）are negative anomaly and Rb/Sr is 0.38～2.08.From the discrimination diagrams for the tectonic settings of granites,Yangshan granites comed from the settings of post collision.There are no clearly different except for the intruding time between two types of granites,and they resulted from a homgenous magma synthesized the revolutional history of district geology and age of granites from earlier studies,we conclued that the Yangshan ultra-large gold deposit formed during the post-collision extension between the North China block and the Yangtze block.