藏西班公湖斑岩铜矿带成矿斑岩地球化学及Pb、Sr、Nd同位素特征

Geochemistry and Pb,Sr,Nd isotopic features of ore-bearing porphyries in Bangong Lake porphyry copper belt,western Tibet

对班公湖铜矿带2个具有代表性的斑岩铜矿床——多不杂铜矿床和尕尔穷铜矿床进行了详细的岩石地球化学和Pb、Sr、Nd同位素特征研究表明,与冈底斯铜矿带相比,该铜矿带含矿斑岩大离子不相容元素的富集程度相对减弱,而高场强元素和重稀土元素的亏损程度明显减轻,轻、重稀土元素的分馏程度减弱,且具有Eu的弱正异常,岩石在氧化性上更强一些;从Pb、Sr、Nd同位素特征来看,班公湖铜矿带含矿斑岩更富含放射性成因铅,143Nd/144Nd比值明显降低,其源区更接近印度洋沉积物区域,表明该铜矿带含矿斑岩的岩浆源区更浅,有更多的地壳物质加入;班公湖铜矿带含矿斑岩形成的构造环境属于活动大陆边缘区域,而冈底斯铜矿带明显偏离了活动大陆边缘区域,表明班公湖斑岩铜矿带形成于碰撞后地壳隆升阶段,而冈底斯铜矿带则形成于碰撞后地壳伸展阶段。

Detailed geochemical and Pb, Sr, Nd isotopic researches on the Duobuza copper deposit and the Garqiong copper deposit were conducted in the Bangong Lake copper belt. The result shows that, compared with the porphyries of the Gandese copper belt, the ore-bearing porphyries of the Bangong Lake copper belt are weaker in the enrichment of large ion lithophile elements （LILE） and are also weaker in the depletion of high-field strength elements and high rare elements, thus having weak positive Eu anomaly. Viewed from Pb, Sr, Nd isotopic features, the ore-bearing porphyries are characterized by the enrichment of radiogenic Pb, the obviously low ratios of 143Nd/144Nd, and the source nearer to the Indian Ocean sedimentary area, indicating that the magma source of the ore-bearing porphyries is much shallower, with the mixture of more crustal materials. The forming tectonic environment of the ore-bearing porphyries in the Bangong Lake copper belt belonged to the active continental ridge, whereas that in the Gangdese copper belt was far away from the active continental ridge. The Bangong Lake porphyry copper belt was formed in a post-collisional crustal up-lift stage, whereas the Gangdise porphyry copper belt in a stage of post-collisional crustal extensional collapse when the crust rose to the maximum height.