西天山喇嘛苏外围铜矿床岩石地球化学及成矿背景研究

Study on Petrogeochemistry and Metallogenic Background of Lamasuwaiwei Copper Deposit in Western Tianshan Orogenic

位于西天山汗吉尕晚古生代岛弧带的喇嘛苏外围铜矿床是该区内新发现最大的铜矿床,与成矿作用密切相关的花岗闪长斑岩、花岗闪长岩为同源岩浆演化形成,且花岗闪长斑岩可能为晚期产物.本区成矿岩体主量、微量及稀土元素地球化学特征表明,其富集Sr、K、Rb、Th,亏损Ta、Nb、P、Ti,Rb/Sr、Nb/Tb、Rb/Ba、Ba/Th比值明显偏低,轻稀土分异明显,出现较弱Eu负异常,显示源区主要来自下地壳,上地壳泥质沉积物混染作用较弱,且俯冲作用下洋壳的贡献较少.岩石地球化学特征指示其为典型的偏铝质钙碱性I型花岗岩,暗示形成于碰撞前的活动大陆边缘环境.结合区域成矿背景,推测本区成矿岩体是在洋壳俯冲作用下交代上覆楔形地幔,诱发下地壳部分熔融的产物,其形成可能与晚古生代赛里木微陆块北缘准噶尔洋持续俯冲作用有关.

The Lamasuwaiwei copper deposit was the newly discovered largest copper deposit, located on Hanjiga late-Paleozoic island arc zone of Western Tianshan orogenic.The rock mass closely related to mineralization,were predominated by granodioritic porphyry and granodiorite,which were formed by comagma, furthermore, granodioritic porphyry may be highly evolved from a relative late magma. The major element、trace element and REE compositions suggest that, they were characterized by enrichment of Sr、K、Rb、Th,opposite to depletion of Ta、Nb、P、Ti, coupled with significantly low Rb/Sr、Nb/Tb、Rb/Ba and Ba/Th, obvious differentiation of LREE and weak Eu negative anomaly,suggesting that they were mainly derived from lower crust, having weaker contamination of argillaceous sediment from upper crust, and having less contribution of subduction from oceanic crust. The geochemical characteristics show that they were the typical quasi-aluminous calc alkaline I-type granite, implied that formed in active continental margin before plate collision. Combined with regional geological background, the formation of the metallogenic rocks were attributed to partial melting of lower crust produced by wedge-shaped mantle metasomatism under the subduction of oceanic crust, and the metallogenic rocks might be related to the sustained subduction of the Junggar ocean in the northern margin of Sailimu micro continental massif during the Late Paleozoic time.