西藏铁格隆南超大型铜(金、银)矿含矿斑岩岩石成因及其对多龙地区早白垩世成矿动力学机制的启示

Petrologic genesis of ore-bearing porphyries in Tiegelongnan giant Cu( Au,Ag) deposit,Tibet and its implications for the dynamic of Cretaceous mineralization,Duolong

铁格隆南是西藏多龙矿集区新发现的超大型斑岩-浅成低温热液型铜(金、银)矿床。作为班公湖-怒江成矿带西段早白垩世重大成矿事件的典型代表,铁格隆南矿床以及整个多龙矿集区的含矿斑岩岩石成因及成矿动力学机制仍存在明显争议。本文以铁格隆南矿床为核心,基于详细的矿床地质特征和岩石学特征,利用锆石的SHRIMP U-Pb年代学厘定花岗闪长斑岩侵位时代为121. 2±2. 4Ma,与区域早白垩世含矿斑岩岩浆侵位时间一致。同时,详细的岩石地球化学分析表明,铁格隆南矿床及多龙矿集区,含矿斑岩以花岗闪长斑岩为主,含少量闪长玢岩和花岗斑岩,属于高钾-钙碱性或钾玄岩系列,富集轻稀土和大离子亲石元素(Rb、Ba、U),亏损重稀土及高场强元素(Nb、Ta、Ti),具典型的弧岩浆特征。此外,其岩石地球化学特征及Sr-Nd-Pb-Hf同位素组成揭示,含矿斑岩的岩浆源区可能与俯冲板片流体交代的富集岩石圈地幔部分熔融有关。最后,详细的岩石学"探针"及区域岩浆活动特征表明,多龙矿集区白垩世重大成矿作用动力学机制与班公湖-怒江洋北向俯冲板片的折返(130～110Ma)有关。

Tiegelongnan is a newly discovered giant porphyry-epithermal copper (gold and silver) deposit in the Duolong ore concentrated area, Tibet. As a typical representative products of the important Early Cretaceous ore-forming event in western part of the Bangong Co-Nujiang metallogenic belt, the petrology and dynamic of the mineralization of the ore-bearing porphyries in this deposit are still in hot debate. Based on detailed geological and petrological characteristics of the Tiegelongnan deposit, the SHRIMP U-Pb chronology data of the zircons showed the emplacement time of the granodiorite porphyry from Tiegelongnan was 121.2±2.4Ma, which was consistent with the magmatic emplacement time of the Early Cretaceous ore-bearing porphyries in Duolong district. At the same time, the detailed petrogeochemical analysis showed that the ore-bearing porphyries in the Tiegelongnan deposit and the Duolong ore concentrated area were mainly granodiorite porphyry, together with minor diorite porphyry and granite porphyry, which belonged to the series of high-K-calc-alkaline or shoshonite. They were enriched in light rare earth elements (LREE) and big ionic lithophilic elements (LILE, e.g. Rb, Ba, U), depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE, e.g. Nb, Ta, Ti), with typical arc magmatic characteristics. Besides, the geochemistry and Sr-Nd-Pb-Hf isotopic compositions revealed that the magmatic source of the ore-bearing porphyries was from Duolong, and it might be related to partial melting of the enriched metasomatized mantle modified by the slab-derived fluids. Finally, the detailed petrological "probes" studies and regional magmatic activity characteristics suggested that the key dynamics of the giant Cretaceous mineralization in the Duolong ore concentrated area might be related to the roll-back of the north-subduction plate from Bangong Co-Nujiang Ocean (130~110Ma).