湘西龙山江家垭铅锌矿床石英Rb-Sr同位素测年与示踪研究

江家垭铅锌矿床位于扬子地台东南缘,红岩溪背斜轴部,是湘西—鄂西铅锌成矿带重要的铅锌矿床之一,铅锌矿体呈似层状和脉状,受地层与构造的控制,主要产于下奥陶统南津关组砂屑灰岩中。文章首次采用超低本底石英Rb-Sr同位素测年方法,对湘西龙山江家垭铅锌矿床主成矿期形成的富铅锌石英脉进行了等时线年龄测定,获得成矿年龄为(372±9.8)Ma,n(87Sr)/n(86Sr)=(0.709409±0.000058)。通过成矿地质背景探讨,认为该矿床的形成与晚泥盆世华南地区发生的拉张断陷导致的盆地流体大规模运动有关。锶同位素初始比值测试结果表明江家垭铅锌矿床成矿物质来源可能主要源自围岩碳酸盐岩,成矿过程中陆壳的影响较为明显。

Rb-Sr dating and tracer study of quartz from the Jiangjiaya lead-zinc deposit in western Hunan

Abstract: The Jiangjiaya Pb-Zn deposit, located on the southeastern margin of the Yangtze craton and along the axis of the Hongyanxi anticline, is an important Pb-Zn deposit in the western Hunan-western Hubei metallogenic belt. The orebody exhibits stratabound and veined forms and is controlled by strata and faults, and the deposit occurs in the Ordovician (Early Paleozoic) Nanjingguan Formation. The ultra-low procedural blanks and Rb-Sr dating of quartz separates yielded an isochron age of (372±9.8) Ma, with n(87Sr)/ n(86Sr) equal to (0.709409±0.000058) for the deposit, which represents the main stage ore-forming age of the deposit. Geological setting indicates that the formation of the deposit was probably related to the late Devonian mass movement of basin fluids resulting from extensional and fault depression in South China. Initial Sr isotope ratios show that the ore materials of the deposit were derived from the host rocks, and the influence of continental crust was obvious in the ore-forming process.