内蒙古阿鲁科尔沁地区早白垩世侵入岩地球化学特征及其成矿潜力

Geochemistry and metallogenic potentiality of Early Cretaceous intrusive rocks in Ar Horqin area,Inner Mongolia

阿鲁科尔沁地区早白垩世侵入岩主要由中细粒花岗闪长岩、中细粒二长花岗岩、花岗斑岩组成,岩体总体具有富硅、富钠而相对贫钾的特征,属准铝质—弱过铝质的钙碱性系列。岩体中稀土元素总量较低,轻重稀土发生分馏,具有明显的Eu负异常,亏损高场强元素Nb、Ta、P、Ti,相对富Th、U、Zr、La和轻稀土元素,相对贫Sr,属I型花岗岩。岩体主体来源于壳源组分的部分熔融,形成于早白垩世的后碰撞伸展环境,为有利成矿构造演化阶段。岩体中,w(K)/w(Rb)比值、w(Rb)/w(Sr)比值、w(Fe_2O_3)/w(FeO)比值、分异指数DI较大,固结指数SI较小,属演化程度低、分异程度较高的氧化型磁铁矿系列花岗岩,其地球化学含矿性参数显示Mo、Cu、Pb-Zn金属成矿潜力依次降低,Au成矿潜力差。

Located in the eastern Central Asian orogenic belt,Ar Horqin area has widely distributed Mesozoic magmatic rocks. In this paper,petrologic and element geochemical studies were carried out for the early Cretaceous intrusive rocks in Ar Horqin area. The study of petrology indicates that the granitoids are mainly composed of granodiorite,adamellite and granite-porphyry. Major element geochemistry shows that the rocks are quasi-aluminous cal-alkaline granites,which are characterized by relatively rich silicon and sodium and poor potassium. Trace elements have a similar variation trend characterized by low REE,fractionation of REE,significant negative anomaly of Eu,depletion of Nb,Ta,P,Ti,and enrichment of LREE,Rb,Th,U,Zr,La. Main body of the granites belongs to calcalkaline I genetic type. The magmas were formed by partial melting of the crust in an extensional setting after the collision,which was a favorable metallogenic tectonic evolution stage. DI values,K / Rb and Rb / Sr ratios are larger,SI values are smaller,and Fe2O3/FeO ratios are also larger,suggesting that the granites belong to low evolution,highly fractionated oxidation type or magnetite series. Their geochemical ore parameters indicate that Mo,Cu,Pb-Zn mineralization potentiality decreases systematically,and Au mineralization potentiality is poorer.