西藏雄村铜金矿I号矿体赋矿凝灰岩成因探讨: 来自 岩石地球化学、Sr-Nd-Pb同位素地球化学特征的证据

雄村斑岩型铜金矿集区位于冈底斯造山带中段南缘,目前发现的Ⅰ、Ⅱ、Ⅲ号主矿体均产于含矿斑岩体及其接触带附近的凝灰岩中,本文主要对雄村I号矿体赋矿凝灰岩开展岩石地球化学特征研究。赋矿凝灰岩显示出与岛弧火山岩相似的地球化学特征,如相对富集LREE、LILE而亏损HREE、HFS以及低的I(Sr)值(变化范围为0.704163～0.705369,均值0.704907)和正的εNd(t)值(变化范围为3.7805～7.6286,均值5.904121)等,其形成与印度-亚洲大陆碰撞造山之前的新特提斯洋俯冲作用有关,产于新特提斯洋向北的洋内俯冲作用而形成的岛弧环境。赋矿凝灰岩起源于岛弧底部的新生玄武质岩层的部分熔融,源岩主要由角闪石、斜长石和少量石榴子石组成。赋矿凝灰岩、含矿斑岩体和成矿作用同属一个火山-岩浆-热液系统,赋矿凝灰岩为成矿提供了必要的围岩外部因素,是矿区重要的控矿因素,也是一个重要的找矿地质条件。在雄村矿区及其外围,侵位于凝灰岩中的斑岩体应该是今后找矿评价的重点区域。

The Genesis of Mineralized Tuff of No. I Ore Body in the Xiongcun Porphyry Copper-Gold Metallogenic Ore District, Tibet: Evidence from Geochemistry and Sr-Nd-Pb Isotopes

The Xiongcun porphyry copper-gold metallogenic ore concentration area is located in the north of the middle Gangdise orogenic belt.No.Ⅰ,Ⅱ and Ⅲ main ore bodies of Xiongcun area are hosted in ore-bearing porphyries and tuff along the contact zone.This paper mainly studied geochemistry of mineralized tuff in Xiongcun No.I ore body.The mineralized tuff is similar to volcanic rocks in island arc in such geochemical characteristics as relative enrichment of LREE and LILE,depletion of HREE and HFS,low I(Sr) values(raning from 0.704163 to 0.705369,0.704907 on average),and positive ε Nd(t) values(ranging from 3.7805～7.6286,5.904121 on average).Mineralized tuff was formed in an island arc environment and was related to northwards subduction of the Neo-Tethys Ocean which occurred before India-Asian continental collision,and its source mainly came from partial melting of the juvenile basaltic strata at the bottom of the island arc.The mineral assemblage of the source region include hornblende,plagioclase and minor garnet.Mineralized tuff,ore-bearing porphyry and metallogenesis belonged to the same volcano-magma-fluid system.The mineralized tuff provided mainly external factors for the mineralization,acted as an important ore-controlling condition and also serves as an important ore-prospecting geological condition.The locations of porphyries emplaced in tuff are key ore-prospecting areas in Xiongcun area and its peripheral areas.