江西九瑞地区东雷湾矽卡岩型铜多金属矿床锆石U-Pb和辉钼矿Re-Os年龄及其地质意义

摘要

东雷湾矽卡岩型铜钼金多金属矿床位于九瑞矿集区西北部。本文利用锆石 LA-MC-ICP MS U-Pb同位素定年方法,对东雷湾的主要岩体花岗闪长斑岩成岩时代进行研究,获得花岗闪长斑岩的锆石U-Pb年龄为(142.24±0.52) Ma；同时采用辉钼矿Re-Os同位素定年方法对矿床石英硫化物中的辉钼矿进行定年,首次获得东雷湾矿床的成矿年龄：6件辉钼矿的Re-Os同位素模式年龄范围为(144.8±3.1)~(147.1±2.4) Ma,加权平均年龄为(146.12±0.97) Ma,等时线年龄为(143.3±5.2) Ma。成岩年龄与成矿年龄在误差范围内一致,存在较短的成岩成矿时差,表明成岩成矿过程连续。辉钼矿的Re含量指示东雷湾矿床的成矿作用与岩浆壳幔混合作用有关。东雷湾矿区的成岩成矿时代与九瑞矿集区典型岩体和矿床的成岩成矿时代相似,同时也与长江中下游地区铜陵、安庆和鄂东南(部分地区)的典型铜多金属矿床的成岩成矿时代基本一致。结合区域地质资料,本文认为东雷湾矿床是中国东部东西向印支期构造域向北东向古太平洋构造域构造体制大转折晚期成矿作用的产物。%The Dongleiwan skarn Cu-Mo-Au polymetallic deposit is located in northwestern Jiujiang–Ruichang ore concentration area. U-Pb LA-MC-ICP MS dating of zircons from Dongleiwan granodiorite porphyry yielded an age of (142.24±0.52) Ma. Six molybdenite samples separated from quartz sulfides in Dongleiwan skarn orebodies were used for Re-Os dating and the model ages obtained range from (144.8±3.1) Ma to (147.1±2.4) Ma, with weighted average (146.12±0.97) Ma and isochron age (143.3±5.2) Ma. These ages suggest that the mineralization in the Dongleiwan skarn copper-polymetallic deposit was genetically associated with the granodiorite porphyry, and the rock-forming and ore-forming processes were quite consistent with each other. The Re content of molybdenite indicates that the ore-forming materials were derived from the mantle and the crust. These data show that ages of rock body and ore body in the Dongleiwan deposit are almost identical with ages of other typical rock masses and deposits in the Jiujiang–Ruichang ore concentration area, and even quite close to ages of typical Cu-polymetallic deposits in such areas as Tongling, Anqing and part of southeast Hubei along the Middle–Lower Yangtze River metallogenic belt. Based on regional tectonic evolution, it is inferred that the Dongleiwan deposit was formed in the transition period from EW-striking Indosinian tectonic domain to NE-striking Paleo-Pacific tectonic domain.