新疆阿尔泰小土尔根铜矿区岩体地球化学及其地质意义

Geochemistry and geological implications of the plutons from the Xiaotuergen copper ore district in Altay,Xinjiang

小土尔根是近年来诺尔特地区新发现的斑岩铜矿。矿区内发育花岗斑岩、花岗闪长斑岩、黑云母二长花岗岩,其中与成矿作用密切相关的岩体为花岗闪长斑岩。为了确定矿区侵入岩成因及其与铜矿化的内在关系,对矿区内发育的岩体开展了岩相学和地球化学研究。结果表明,所有岩石富硅和碱,铝含量中等,属高钾钙碱性和钾玄质系列岩石。所有样品富集Rb、Ba等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、Ti、P、Sr和重稀土元素,指示其为同源岩浆分异演化的产物,形成于陆缘弧环境。结合区域地质背景,推测这些岩体是俯冲洋壳发生部分熔融并交代上覆地幔楔后,在上升过程中经分离结晶作用后的产物。与典型的还原性斑岩型铜矿形成条件进行对比研究后,认为小土尔根地区有形成斑岩型矿床的潜力。

Xiaotuergen is the first porphyry copper deposit discovered in Nuoerte area in recent years. Granite porphyry,granodiorite porphyry and biotite monzonitic granite are widely developed in the ore district,and the mineralization is closely related to the granodiorite porphyry. In order to investigate the petrogenesis of intrusive rocks and their intrinsic relationship with copper mineralization,the authors carried out the petrographic and geochemical studies of the widely developed intrusive rocks in the ore district. The results show that all rocks exhibit high silica and alkaline,with moderate aluminum content. They belong to high-K calc-alkaline and shoshonitic rocks. All samples are enriched in Rb,Ba and other large ion lithophile elements（ LILE） and LREE,and relatively depleted in Nb,Ta,Ti,P,Sr and HREE,indicating that they were formed by comagmatic differentiation and evolution in a continental arc environment. Combined with regional geological background,the authors hold that these rocks are the product of subducted oceanic crust which experienced partial melting,replacement of overlying mantle wedge and fractional crystallization during the rising process. A comparison with the formation conditions of typical reduced porphyry copper deposits shows that the Xiaotuergen ore district has the potential to form porphyry deposit.