湖南花垣矿集区李梅铅锌矿床闪锌矿Rb-Sr定年与成矿物质示踪

李梅铅锌矿床位于扬子克拉通东南缘花垣矿集区北段,预测铅锌储量为300×10⁴ t,是该区铅锌矿床的典型代表。该矿床铅锌矿体呈层状、似层状,受地层与构造的控制,主要赋存于下寒武统清虚洞组下段第三亚段地层藻灰岩中。为获得该矿床的成矿年龄,探讨其成矿物质来源,采用闪锌矿Rb-Sr定年方法,对主成矿期形成的闪锌矿单矿物进行Rb-Sr同位素组成测定,获得的等时线年龄为(464±12)Ma(平均标准权重偏差为0.97),成矿时代为中奥陶世,成矿早于花垣矿集区南段的狮子山铅锌矿床(成矿时间为(410±12)Ma)和柔先山铅锌矿床((412±6)Ma),推断在花垣矿集区范围内发生了郁南运动和广西运动导致的两期成矿事件,整个矿集区成矿时限跨度大约为70 Ma。李梅铅锌矿床成矿时代明显晚于赋矿地层时代,该矿床的形成可能与郁南运动形成伸展构造引起的构造热液活动有关。闪锌矿的⁸⁷Sr/⁸⁶Sr值为0.709 56～0.711 14,(⁸⁷Sr/⁸⁶Sr)_i值为0.709 380±0.000 018,成矿流体具有高于赋矿围岩的高Sr同位素比值,推断成矿物质应主要源自具有高⁸⁷Sr/⁸⁶Sr值和高Pb、Zn丰度的下伏寒武系石牌组和牛蹄塘组。

Rb-Sr Dating and Ore-forming Material Tracing of Sphalerite from Limei Pb-Zn Deposit in Huayuan Ore Concentration Area of Hunan,China

Limei Pb-Zn deposit is located in the northern part of Huayuan ore concentration area, the southeastern margin of Yangtze craton with a predicted reserve of 300×10⁴ t, which is the most typical Pb-Zn deposit in this area. The ore bodies in Limei Pb-Zn deposit are stratiform and stratoid, which are controlled by the strata and structures. They mainly occur in the algal limestone of the third sub-member of Lower Cambrian Qingxudong Formation. In order to obtain the metallogenic age of Limei Pb-Zn deposit and discuss the source of ore-forming materials, the isochron age of monomineral sphalerite formed in the main metallogenic period was yielded by Rb-Sr dating method. The obtained age is(464±12)Ma(MSWD is 0.97). The metallogenic epoch is Middle Ordovician, and the mineralization is earlier than that of Shizishan Pb-Zn deposit((410±12)Ma)and Rouxianshan Pb-Zn deposit((412±6)Ma)in the southern part of Huayuan ore concentration area. It is inferred that there are two metallogenic events in Huayuan ore concentration area caused by Yunan movement and Guangxi movement. The metallogenic time span of the whole ore concentration area is about 70 Ma. The mineralization age of Limei Pb-Zn deposit is obviously later than that of the host strata; the formation may be related to the tectonic hydrothermal activity caused by the extension structure during Yunan movement. The ⁸⁷Sr/⁸⁶Sr ratio of sphalerite ranges from 0.709 56 to 0.711 14, and the(⁸⁷Sr/⁸⁶Sr)_i is 0.709 380±0.000 018. The ore-forming fluid has a high Sr isotope ratio, which is higher than that of the host rock. It is inferred that the ore-forming materials should mainly come from the underlying Cambrian Shipai Formation and Niutitang Formation with high ⁸⁷Sr/⁸⁶Sr ratio and high abundances of Pb and Zn.