兰坪盆地西缘沉积岩容矿脉状Cu-Ag-Pb-Zn多金属矿床成矿时代

摘要

兰坪盆地是中国著名的三江构造-成矿带的重要组成部分。兰坪盆地西缘发育大量沉积岩容矿脉状Cu-Ag-Pb-Zn多金属矿床，矿体的分布受一个逆冲推覆构造控制。逆冲推覆构造的根部带主要发育脉状Cu-Ag（Mo）矿床（包括金满Cu-Ag、连城Cu-Mo及一系列脉状Cu矿床）；前锋带主要发育Pb-Zn-Ag（±Cu）矿床（包括白秧坪Pb-Zn-Ag-Cu多金属矿集区及一系列小型的Pb-Zn矿床)。为了探讨兰坪盆地西缘脉状Cu-Ag-Pb-Zn多金属矿床成矿时代，该文在系统总结前人年代学数据的基础上，补充进行了金满Cu矿床与黄铜矿密切共生的方解石的Sm-Nd法和连城Cu-Mo矿床成矿早阶段辉钼矿的Re-Os法测年。金满Cu矿床方解石Sm-Nd等时线年龄为58±5 Ma，连城Cu-Mo矿床Re-Os年龄为48±2 Ma，结合前人的资料表明：（1）根部带Cu矿床主成矿时代为56~48 Ma，对应于印度—亚洲大陆碰撞造山主碰撞阶段，后期（47~35 Ma）很可能存在一期Cu-Ag（Mo）的叠加或改造成矿作用；（2）前锋带Pb-Zn-Ag（±Cu）多金属矿床的成矿作用主要发生在31~29 Ma左右，对应于印度—亚洲大陆碰撞造山的晚碰撞构造转换期。%The Lanping basin is a significant Pb-Zn-Cu-Ag mineralization belt of the Sanjiang Tethyan metallogenic province in China. A series of sediments-hosted Himalayan Cu-Ag-Pb-Zn polymetallic deposits have been discovered in the western part of the basin, which are controlled by a thrust-nappe system. In the thrust-nappe system, the Cu orebodies occur as vein-type deposits in the western and relatively deep part of the mineralization system (the root zone), mainly including the Jinman Cu-Ag deposit, Liancheng Cu-Mo deposit, and more than 30 small vein copper deposits, such as Kedengjian, Huangbai, and Enqi. The Pb-Zn-Ag(± Cu) orebodies mainly occur in the eastern and relatively shallow part of the system (the front zone), including the Baiyangping Pb-Zn-Ag-Cu ore belt, and some small Ag-bearing Pb-Zn deposits, such as Liziping and Wudichang. To define the metallogenic history of the Cu-Ag-Pb-Zn polymetallic deposits in western Lanping basin, we dated nine calcite samples associated with copper sulfide from the Jinman Cu deposit by the Sm-Nd isotopic analysis and five molybdenite samples from the Liancheng Cu-Mo deposit by the Re-Os isotopic analysis. The nine calcite samples yielded an age of 58.2 ± 5.3 Ma (2σ, MSWD=0.039). The five molybdenite samples yielded an isochron age of 47.8±1.8 Ma (2σ, MSWD=7.2). The Sm-Nd isotopic age of calcites from the Jinman deposit (58 ±5 Ma) and the molybdenite Re-Os age for the Liancheng deposit (48 ± 2 Ma), together with previously published chronological data, demonstrate that (1) the main Cu-Ag (Mo) mineralization in the root zone took place at ca. 56~48 Ma, corresponding to the main-collisional stage of the Indo-Asian collision orogeny;Possibly, there was a remobilization or a new phase of Cu mineralization in the duration from 35 to 47 Ma; (2) The main Pb-Zn-Ag (± Cu) mineralization in the front zone took place at ca. 31~29 Ma, corresponding to the late-collisional stage of the Indo-Asian collision orogeny.