| 闪锌矿、方铅矿的Re-Os同位素定年在典型铅锌矿床中的应用 | |
| 刘莹莹 | |
| Thesis Advisor | 漆亮 |
| 2014 | |
| Degree Grantor | 中国科学院研究生院 |
| Place of Conferral | 北京 |
| Degree Name | 博士 |
| Degree Discipline | 地球化学 |
| Keyword | Re-os同位素定年 川－滇－黔铅锌成矿域 典型铅锌矿床 闪锌矿 方铅矿 |
| Abstract | 铅锌矿床定年一直是国内外地学界的难题。由于不同矿床的实际情况不同，很难找到一种通用而有效的定年方法。近年来，Re-Os同位素方法被广泛应用于热液硫化物矿床定年。黄铁矿虽在铅锌矿床中普遍存在，但期次较多，不易判别是否为成矿期的产物。闪锌矿和方铅矿是铅锌矿床Re-Os同位素定年的有效矿石矿物，但其Re含量较低且变化范围大，当用常规阴离子交换树脂方法进行分离富集时Re回收率严重偏低。针对以上问题，本研究应用改进的Carius管方法系统开展了闪锌矿和方铅矿样品的Re、Os测试方法的研究。并成功应用于典型铅锌矿床的闪锌矿和方铅矿Re-Os同位素定年，结合部分矿床金属硫化物样品的硫同位素及微量元素的数据，有效探讨矿床成因。研究主要取得了如下成果： （1）考察了影响Re回收率的各种因素，确定了Re在闪锌矿和方铅矿样品的预处理过程中丢失的具体原因。对于闪锌矿，基体中大量存在的Zn2+严重影响了(ReO4)-的阴离子交换；而对于方铅矿，基体中大量存在的Pb2+未影响(ReO4)-的阴离子交换，逆王水分解产物PbSO4等铅盐白色沉淀也未导致Re的大量丢失，而2N HCl介质的阴离子交换溶液中同时存在的PbSO4和ZnSO4严重影响了Re的正常回收。 （2）提出了解决方案。通过使用HCl预溶或在溶样时添加少量（~0.1 g）Zn2+，Fe3+等阳离子的方法可以显著提高方铅矿样品的Re回收率，但仍存在一定缺陷；而改用0.8 N HNO3介质进行阴离子交换，不仅能有效提升Re回收率、对Os同位素分析无任何影响，而且对0.1-3.0 g称样量范围内的方铅矿和闪锌矿样品均有较好的适用性，提高了Re的回收率，并简化了分析流程。 （3）利用改进的分析方法对川－滇－黔地区的典型MVT铅锌矿床进行了硫化物Re-Os同位素定年的尝试。杉树林，天桥和金沙厂等铅锌矿床的硫化物Re含量均低于2.0 ng/g；云南会泽（Re~3.47-588 ng/g），富乐（Re~3.52-398 ng/g）和毛坪（Re~1.29-89.05 ng/g）等滇东北地区铅锌矿床硫化物Re含量相对较高且变化范围大，普通Os含量相对较低（< 0.1 ng/g），为典型的LLHR（low-level highly radiogenic）硫化物。 （4）川－滇－黔铅锌成矿域的定年结果显示，毛坪铅锌矿床的Re-Os等时线年龄为55.2±3.5 Ma (2σ，MSWD=0.47)；富乐铅锌矿床的浅色和深色闪锌矿分别获得34.7±4.4 Ma (2σ，MSWD=2.9)和20.4±3.2 Ma (2σ，MSWD=3.9)两个等时线年龄；会泽铅锌矿床的硫化物187Re-187Os同位素模式年龄跨度较大，为15.1-147 Ma。川－滇－黔地区定年矿物的S同位素均显示膏盐地层的来源。该区铅锌矿床的Re-Os同位素年龄均揭示了燕山－喜山期的热液作用。 （5） 会泽铅锌矿床中硫化物的Re含量明显受矿物种类控制，在同一样品中，黄铁矿的Re含量比闪锌矿高，且细粒黄铁矿的Re含量明显高于粗粒黄铁矿。部分硫化物样品的微量元素测试结果显示，Ag、Sb、V、Co、Rb、Zr、Ba、Tl、Th和U在细粒黄铁矿中的含量也高于粗粒黄铁矿。 （6） 澜沧老厂铅锌矿床的矿石矿物Re-Os同位素的定年结果得到308±25 Ma (2σ, MSWD=1.04)的等时线年龄和约0.88±0.42的187Os/188Os初始比值，该年龄与围岩（石炭纪凝灰岩）的锆石U-Pb年龄（312~320 Ma）一致，指示其为典型的VHMS成因，所得的初始Os同位素比值也指示了成矿物质的壳幔混合来源。 |
| Other Abstract | Dating of Pb-Zn deposit is always a difficult problem to geologists at home and abroad. Due to the various types of Pb-Zn deposits, it is hard to figure out a general and effective method for dating these deposits. In recent years, Re-Os dating method has been widely applied to hydrothermal deposits. Although pyrite is common in Pb-Zn ores, it has multiple generations so that distinguishing pyrite from the ore-forming stage is difficult. Sphalerite and galena are the effective ore minerals for Re-Os dating of Pb-Zn deposits. However, Re concentration of sphalerite and galena is relative low and varies widely for different types of Pb-Zn deposits. Moreover, experimental studies have shown that the recovery of Re in sphalerite and galena samples is extremely low using routine anion exchange method. To solve the above problems, we carry out a systematic research using the re-usable Carius tube to determine Re and Os in sphalerite and galena. The revised method was used to date some typical Pb-Zn deposits. Combined with sulfur isotopes and trace element compositions of sulfides, the Re-Os results are used to reveal the genesis of the Pb-Zn deposits. The main conclusions are listed as follows. (1) By investigating the various factors affecting the recovery of Re, the key factor for loss of Re during chemical preparation is known. With respect to sphalerite, the abundant Zn2+ in matrix severely prevents the efficiency of anion exchange of (ReO4)-. However, the abundant Pb2+ in galena matrix does not significantly influences the anion exchange of (ReO4)-, and the white precipitation (mainly PbSO4) forming at the dissolving stage (by revise aqua regia) dose not lead to the loss of Re. Therefore, both PbSO4 and ZnSO4 in the medium of 2N HCl that severely lower the recovery of Re. (2) Experimental studies have shown that pre-dissolving samples by HCl or adding ~0.1 gram of Zn2+ or Fe3+ into the samples can significantly improve the recovery of Re in galena matrix, but these methods have some limits. Applying 0.8 N HNO3 medium for anion exchange not only can improve the recovery of Re in galena without any effects on determination of Os, but also can be suitable for 0.1-3.0 grams of sphalerite samples. (3) The revised method is applied to typical MVT Pb-Zn deposits in the famous Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province in southwest China. Pb-Zn sulfides in Shanshulin (杉树林), Tianqiao (天桥) and Jinshachang (金沙厂) deposits contain low Re of < 2.0 ng/g. However, sulfides from the Huize (会泽; Re~3.47-588 ng/g), Fule (富乐; Re~3.52-398 ng/g) and Maoping (毛坪; Re~1.29-89.05 ng/g) Pb-Zn deposits have relatively higher and more varied concentrations of Re, with relative lower common Os (< 0.1 ng/g), typical LLHR (low-level highly radiogenic) sulfides in these deposits. (4) The Maoping (毛坪) Pb-Zn deposit has a Re-Os isochron age of 55.2±3.5 Ma (2σ，MSWD=0.47). The light and dark sphalerites of the Fule (富乐) Pb-Zn deposit yielded isochron ages of 34.7±4.4 Ma (2σ，MSWD=2.9) and 20.4±3.2 Ma (2σ，MSWD=3.9), respectively. The Huize (会泽) Pb-Zn deposit has 187Re-187Os model ages ranging from 15.1 to 147 Ma, which indicates hydrothermactivities during Yanshanian and Himalayan periods. (5) Pyrites from the Huize (会泽) Pb-Zn deposit have higher Re concentration than sphalerites, and the fine-grained pyrites concentrate more Re than coarse-grained pyrites. The Ag, Sb, V, Co, Rb, Zr, Ba, Tl, Th, and U are also higher in fine-grained pyrites than coarse-grained pyrites. (6) For the Laochang (老厂) Pb-Zn deposit in Lancang (澜沧), the Re-Os isotope data of sphalerite and galena yield an isochron age of 308±25 Ma (2σ, MSWD=1.04) and initial 187Os/188Os of ~0.88±0.42. The Re-Os age of the Pb-Zn ore is in agreement with the age of the country rock (312~320 Ma；zircon U-Pb), indicating that the deposit is a typical VHMS type. The initial 187Os/188Os ratio indicates a mixed source of mantle and crust. |
| Subject Area | 矿床地球化学 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/5873 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 刘莹莹. 闪锌矿、方铅矿的Re-Os同位素定年在典型铅锌矿床中的应用[D]. 北京. 中国科学院研究生院,2014. |
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