湘东北地区金矿成矿时代研究

Ore-forming epoch of gold deposits in northeastern Hunan

产于中元古界冷家溪群浅变质碎屑岩中的一系列金矿床是湘东北地区主要金矿床类型。早期研究者认为该类金矿床的成矿时代属加里东期或燕山期,但均没有高质量的测年数据支持。笔者对湘东北地区黄金洞、万古、团山背3个典型金矿床开展了石英流体包裹体Rb-Sr同位素测年工作,获得黄金洞、万古和团山背3个金矿床Rb-Sr等时线年龄,分别为(462±18)Ma(MSWD=1.6)、(425±33)Ma(MSWD=0.14)和(222.4±9.4)Ma(MSWD=2.6),87Sr/86Sr初始值分别为(0.7589±0.0005)、(0.7517±0.0004)和(0.7335±0.0009)。测年结果表明,湘东北地区金成矿主要发生在加里东期,并存在印支期金成矿作用。此外,湘东北地区与湘西地区金矿床成矿时代具有一致性,均集中于加里东期和印支期,是江南古陆上金矿床成矿的两个主要时期。

Gold deposits in northeastern Hunan are mainly hosted in epimetamorphic clastic rocks of Middle Proterozoic Lengjiaxi Group.It was thought by some earlier researchers that gold mineralization took place in Caledonian or Yanshanian epoch,which,however,was not supported by high-quality age data.In this paper, the Rb-Sr isochron of fluid inclusions trapped in quartz was used to date the ore-forming epochs of gold deposits.The Huangjindong,Wangu and Tuanshanbei gold deposits are dated at（462±18） Ma（MSWD=1.6）,（425±33） Ma（MSWD=0.14） and（222.4±9.4） Ma（MSWD=2.6） respectively,with（^87Sr/^86Sr）i being（0.7589±0.0005）,（0.7517±0.0004） and（0.7335±0.0009）.Dating results show that gold mineralization in northeastern Hunan mainly occurred in Caledonian,with Indosinian probably being the other metallogenic epoch.In addition,gold ore-forming epochs of western Hunan and northeastern Hunan were likely concentrated in Caledonian and Indosinian,implying that Caledonian and Indosinian were the two main ore-forming epochs in Jiangnan terrain.