过铝质成铜岩体的成因及对斑岩铜矿成矿物质来源的指示—以西藏雄梅铜矿成矿岩体为例

Bangonghu-Nujiang metallogenic belt is an important copper polymetallic matallogenic belt newly discovered in China. A stage of peraluminous to strongly peraluminous granitoids are produced in this metallogenic belt. Including ore-bearing intrusion of the Xiongmei porphyry copper deposit，many copper deposits have closed relations with these peraluminous granitoids. .Typical porphyry copper deposit forms during the subdution of the oceanic slab and is related to the calcium-alkaline and metaluminous-weakly peraluminous magma, whereas the early Cretaceous copper deposits in Bangonghu-Nujiang metallogenic belt generally have affinity with peraluminous magma. The reason why the ore-bearing granitoids are peraluminou is the key to understand the genetic mechanism of the copper deposits in the Bangonghu-Nujiang metallogenic belt. Through petrography, element geochemistry and isotopic geochemistry, this project will choose the Xiongmei ore-bearing intrusion as the research object and try to interpret petrogenesis of the peraluminous rocks and specific genetic mechanism of the copper deposits in the Bangonghu-Nujiang metallogenic belt. Therefore, esearch on the petrogenesis of the ore-bearing intrusion of the Xiongmei porphyry cupper deposit can not only understand the genetic mechanism of the Bangonghu-Nujiang metallogenic bel and guide ore prospecting, but also enrich the theory of the porphyry copper deposit.

班公湖-怒江成矿带是我国新发现的一条重要的铜多金属成矿带。带内早白垩世发育有一期过铝质-强过铝质的岩浆事件，包括雄梅斑岩铜矿在内很多铜矿均与该期过铝质花岗类有密切关系。典型斑岩铜矿主要形成于洋片俯冲阶段，与钙碱性偏铝质-弱过铝质岩浆有关，而班怒带早白垩世铜矿床成矿岩体普遍具有过铝质的特点，是什么原因导致了成矿岩体具有强富铝的特点？这是理解班公湖-怒江成矿带铜矿的形成机制的关键。本项目拟选取班怒带中段的雄梅铜矿成矿岩体作为研究对象，综合运用岩相学、元素地球化学及同位素地球化学来探讨成矿岩体的岩石成因，进一步研究这类具有过铝质特点斑岩铜矿的成矿机制。因此，研究雄梅铜矿过铝质成矿岩体不仅可以理解班公湖-怒江成矿带铜矿形成机制，指导找矿实践，而且可以丰富斑岩铜矿的成矿理论。

目任务书设立的研究目标通过研究雄梅铜矿过铝质成矿岩体的岩石成因，判断在俯冲相关的构造背景下，洋底沉积物是否为造成成矿岩体过铝质根本原因，进一步限定班公湖-怒江成矿带中段斑岩铜矿的成矿物质来源和地球化学动力学背景，丰富斑岩型铜矿的成矿理论及指导找矿工作。.雄梅岩体的岩石成因研究：选取新鲜无矿化的岩石样品粉碎至200目，首先对岩石样品进行硅酸盐全分析，依据硅酸盐全分析结果，选择其中代表性岩石样品进行微量元素和稀土元素分析，参照岩相学和主量元素研究结果，探讨雄梅含矿岩体岩石化学性质和岩石成因。结合Rb、Sr、Sm、Nd 元素含量，分散选取适合的样品，进行全岩Sr-Nd-Pb 同位素分析。根据锆石定年的结果，选区合适的锆石颗粒进行锆石原位Lu-Hf-O 同位素测试，探讨雄梅含矿岩体成岩物质来源。尤其Pb同位素具有灵敏的“块体效应”，而且在洋底沉积物中富集，可与“现在的特提斯洋”印度洋沉积物进行对比，同时，Nd-Hf 同位素联合示踪，两者之间是否存在解耦也是示踪泥质沉积物的有效手段。通过以上研究，深入开展雄梅过铝质岩体的岩石成因，进一步探讨铜矿的成矿物质来源及成矿机制，阐明雄梅铜矿成矿作用的地球化学动力学背景，并尝试将上述研成果推广应用于整个班公湖-怒江成矿带成矿理论研究和找矿实践中。