| 湘西花垣矿集区狮子山铅锌矿床闪锌矿Rb-Sr定年及地质意义 |
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| 引用本文： | 段其发,曹亮,曾健康,周云,汤朝阳,李堃.湘西花垣矿集区狮子山铅锌矿床闪锌矿Rb-Sr定年及地质意义[J].地球科学,2014,39(8):977-986. |
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| 作者姓名： | 段其发 曹亮 曾健康 周云 汤朝阳 李堃 |
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| 作者单位： | 1.中国地质大学地球科学学院, 湖北武汉 430074 |
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| 基金项目： | 中国地质调查局大调查项目(No.1212010632005);地质矿产调查评价专项(No.1212011120790) |
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| 摘 要： | 花垣矿集区位于扬子地块东南缘与雪峰(江南)造山带的过渡部位, 是湘西-鄂西成矿带的重要组成部分.狮子山铅锌矿床的发现是近年来湘西-鄂西成矿带矿地质勘查的重大进展之一, 该矿床位于矿集区中部, 主矿体呈层状、似层状展布, 与地层产状一致, 直接容矿围岩为下寒武统清虚洞组下段第三亚段藻灰岩, 矿体与围岩界线截然, 伴有方解石化等热液蚀变, 矿石矿物成分相对简单, 主要为闪锌矿, 少量方铅矿和黄铁矿.采用全溶方法和流体包裹体淋滤法对该矿床主成矿期的闪锌矿及其残渣进行Rb-Sr等时线法定年, 获得矿物相+残渣相的年龄为410±12 Ma(MSWD=2.20), 地质时代为早泥盆世, 明显晚于赋矿地层的时代.据此认为矿床的形成可能与加里东运动后构造伸展引起的盆地流体运移有关.该年龄对于整个花垣矿集区的铅锌成矿时代具有同样约束意义.闪锌矿+残渣的Sr初始值(87Sr/86Sr)i为0.709 16, 高于赋矿围岩, 与上覆寒武系白云岩地层的87Sr/86Sr值相近, 表明矿床形成时有来自上覆地层物质的加入.结果表明, 采用闪锌矿Rb-Sr等时线定年方法通过单矿物及其残渣相互约束, 可以有效确定成矿时代.
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| 关 键 词： | 沉积 包裹体 闪锌矿Rb-Sr定年 等时线年龄 成矿时代 狮子山铅锌矿 花垣矿集区 矿藏 |
| 收稿时间： | 2014-04-20 |
Rb-Sr Dating of Sphalerites from Shizishan Pb-Zn Deposit in Huayuan Ore Concentration Area,Western Hunan,and Its Geological Significance |
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| Abstract: | The Huayuan ore concentration area in the western Hunan Province, located in transitional zone between the southeastern margin of Yangtze block and the Xuefeng (Jiangnan) orogenic belt, is important section of the Xiangxi-Exi metallogenetic belt, and is the only one which occurs in limestone of Lower Cambrian strata in the Yangtze block. The Shizishan Pb-Zn deposit which was one of recently discovered Pb-Zn deposits in Xiangxi-Exi metallogenetic belt is located in the center of the Huayuan ore concentration area, and its main ore bodies occur in stratoid with the same trending as the strata and are sharply bounded by wall rocks with weak hydrothermal alteration such as calcitization. Ore bodies are strictly controlled by algal limestone of the third section of the lower member of the Lower Cambrian Qingxudong Formation. Ore minerals are mainly sphalerite, and a small amount of galena and pyrite, whereas gangue mineral is mainly calcite, and a small amount of barite and fluorite. Using the total-sample-dissolution method and leaching method to sphalerite in the Shizishan Pb-Zn deposit for Rb-Sr isochron dating. The isochron ages are obtained 410±12 Ma (MSWD=2.20) with initial 87Sr/86Sr value of 0.709 16 for mineral-phase+residue phase, which shows that the Early Devonian is the main time for the formation of the Shizishan Pb-Zn deposit. Research results indicate that the formation of the deposit is probably related to the regional migration of the basin fluid when the crust is stretched behind the Late Caledonian tectonic movement in Early Devonian, and the age is also a constraint on the Pb-Zn ore-forming time of the whole Huayuan ore concentration area. The initial 87Sr/86Sr value of the mineral phase+residue phase is 0.709 16, which is slightly higher than those of the ore-bearing limestone, and close to those of the overlying dolostone of Middle-Upper Cambrian strata, indicating that the ore-forming materials of the ore bodies in the Shizishan Pb-Zn deposit are possibly derived from the overlying dolostone strata. It is thus concluded that direct dating of the ages of metal minerals by using Rb-Sr isochron method for single minerals and mineral residues could serve as a routine dating method. |
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