新疆东天山寨北山铜矿区火山岩地球化学特征及地质意义

新疆东天山觉罗塔格构造带南缘寨北山铜矿区出露的下石炭统雅满苏组火山岩以中酸性火山岩为主,岩石类型包括安山玢岩和流纹岩,夹少量玄武安山岩以及同成分的火山碎屑岩。岩石主要为钙碱性系列,具富铝(Al_2O_3=12.23%~18.17%,平均15.5%)、低钛(TiO_2=0.12%~1.1%,平均0.55%)的特征;稀土元素整体上呈现轻稀土相对富集、重稀土相对亏损的右倾型稀土配分模式,富集K、Rb、Pb、Th等大离子亲石元素(LILE)、亏损Nb、Ta、Ti等高场强元素(HFSE);Ta/Yb值、Zr/Nb值、Zr/Y值分别为0.10~0.27、15.97~38.34和4.11~12.55。其可能形成于早石炭世古康古尔洋向南俯冲作用的岛弧环境,为俯冲洋壳与地幔楔岩石交代反应的产物。铜矿体赋存于雅满苏组火山岩中,虽与铁矿的赋矿地层雅满苏组时代相同,但赋矿火山岩岩石类型和地球化学特征不同,铜矿床含矿岩体可能是板片俯冲下大洋板片熔融,在岩浆熔融上升过程中同时析出金属,与地幔楔发生交代作用,在合适位置富集成矿。

Geochemical characteristics of the volcanic rocks of Zhaibeishan copper deposit in eastern Tianshan, Xinjiang and its geological implication

The Zhaibeishan copper deposit is located in the southern Jueluotage tectonic belt, Eastern Tianshan, Xinjiang. The volcanic rocks of Low Carbonaceous Yamansu Formation dominated with the middle- felsic volcanic, such as andesitic porphyrite and rhyolite, minor basaltic andesite and its volcanic clasts. The volcanics belong to calc -alkaline rock series which are characterized with high Al₂O₃ content(Al₂O₃ average 15.5%) and low TiO₂ content. The Al₂O₃ content ranges from 12.23% to 18.17% with an average of 15.5%; the TiO₂ content ranges from 0.12% to 1.1% with an average of 0.55%. The REE distribution pattern shows rightward heeling style with enriched total LREE and relative depleted total HREE. The trace element is characterized with enriched LILE group (K, Rb, Pb and Th) and depleted HFSE group (Nb, Ta, and Ti). The ratio of Ta/Yb, Zr/Nb and Zr/Nb ranges from 0.10 to 0.27,5.97 to 38.34 and 4.11 to 12.55 respectively. Based on geochemical study, it indicates that volcanics of Yamansu Formation were formed in the island arc setting, which related to southward subduction of Paleo- Kangguer oceanic lithosphere in early Carboniferous period. The characteristics of REE and trace element show that volcanics are contaminated by the mantle wedge. Although copper ore body and iron ore body were both hosted in volcanics of Yamansu formation, rock types and geochemical characteristics are different. The copper-bearing intrusion was derived from the subducted oceanic slab. During the rising process of magma, metallogenic elements were released by the metasomatism with mantle wedge and deposited in the favorable position to form the copper deposit.