西藏铁格隆南超大型浅成低温热液铜（金、银）矿床的形成时代及其地质意义

摘要

铁格隆南(荣那)矿床位于西藏班公湖—怒江成矿带西段的多龙整装勘查区内,是西藏首例超大规模的浅成低温热液-斑岩型Cu(Au、Ag)矿床。目前,矿床的勘查工作和科学研究正同时展开,本文采用锆石U-Pb、辉钼矿 Re-Os 同位素定年技术,结合系统的钻孔地质编录,对编录中新发现的含矿石英闪长玢岩和辉钼矿进行了高精度同位素测年。石英闪长玢岩LA-ICP-MS锆石U-Pb模式年龄为(120.2±1.0) Ma；辉钼矿Re-Os同位素测年的模式年龄分布在117.8~119.4 Ma范围内,平均模式年龄为(118.5±0.8) Ma,等时线年龄为(119.0±1.4) Ma(MSWD=0.34)。成岩成矿年龄近于一致,成矿略晚于成岩年龄,表明二者属于同一斑岩-浅成低温热液成矿系统。辉钼矿187Re 的含量分布于230.47~1226.6μg/g,指示成矿物质具幔源特征,暗示铁格隆南巨量金属物质的聚集可能与壳幔边界岩浆作用有关。对比研究表明,铁格隆南成矿作用与多不杂、波龙铜(金)矿床一同受控于统一的构造-岩浆成矿系统,该系统的形成无疑与早白垩世班公湖—怒江洋盆向北俯冲有关。%The South Tiegelong (Rongna) deposit, the first superlarge epithermal porphyry Cu (Au, Ag) deposit discovered in Tibet, is situated in the Duolong ore district along the west segment of the Bangong Co–Nujiang River metallogenic belt of Tibet. Both the exploration work and the scientific study of this deposit are being carried out at present. In combination with scientific geological logging, the authors applied the zircon U-Pb and molybdenite Re-Os isotopic dating to the newly found mineral-bearing quartz diorite porphyry and molybdenite. The LA-ICP-MS zircon U-Pb dating of the porphyry yielded a petrogenic age of (120.2±1.0) Ma, and the Re-Os isotopic model ages of molybdenite are distributed in the range of 117.8~119.4 Ma, which vary limitedly with an average model age of (118.45±0.76) Ma. The Re-Os isochron age is (119.0±1.4) Ma (MSWD=0.34). The petrogenic age and the metallogenic age are very close to each other, with the metallogenic age slightly later than the petrogenic age, which indicates that the rock-forming process and the ore-forming process belonged to the same porphyry-epithermal metallogenic system. The values of 187Re, ranging from 230.47 to 1226.6 (μg/g), imply that ore-forming materials were derived from the mantle and the aggregation of the massive metal materials was probably related to the magmatism which happened along the boundary between the mantle and the crust. A comparative study reveals that the mineralization of the South Tiegelong deposit was controlled by the same tectonomagmatic metallogenic system as that of the Duobuza and Bolong porphyry copper-gold deposit. The formation of this system was undoubtedly related to the northward subduction of the Bangonghu–Nujiang Ocean Basin in Early Cretaceous.