利用激光微区分析技术示踪成矿过程

发布时间：2017-12-26 15:54

本文关键词：利用激光微区分析技术示踪成矿过程　出处：《南京大学》2017年博士论文　论文类型：学位论文

【摘要】：本研究主要介绍了激光剥蚀等离子体质谱联用分析技术方法的开发,以及如何将这些方法运用到示踪矿床的成矿过程中去。根据作者有限的知识面,对各种方法分析所面临的局限性和适用范围做了简单评估,文中包含大量技术细节,如:数据的处理,仪器的设置等。本文涉及到的方法,一部分为全新的方法,另一部分的方法是比较成熟,目前已经被国际同行广泛采用的方法。仅从应用的角度,这些方法似乎已经够用,但是从分析的角度去解读,这些方法里涉及到的分析过程中的元素或同位素之间分馏机理尚不明确。所以本研究,除了进行新分析方法的开发以外,也尝试进行一些分析过程中元素和同位素分馏机制方面的研究。本文详细评估了激光参数对硫同位素分析产生的影响,以黄铁矿为例,发现利用193nm ArF准分子激光的不同激光参数分析硫同位素可以产生高达2‰的分馏。为了弄清楚其分馏机制,将剥蚀出的气溶胶颗粒收集起来使用扫描电镜和透射电镜观察,发现黄铁矿在激光剥蚀过程中发生分解,分解成两种相态的物质,一种是陨硫铁单晶,另一种是无定型硫。硫同位素和微量元素在两相之间的分配不同。这两物质被吹送到质谱中的能力存在差异,于是产生了硫同位素和微量元素的分馏。黄铁矿在激光剥蚀过程中行为很特殊,因为在常压下无法使得黄铁矿熔融,最终剥蚀出的气溶胶是纳米级的陨硫铁单晶小球和无定型硫的混合物,而磁黄铁矿气溶胶中收集到的颗粒粒径远远大于黄铁矿的气溶胶的粒径,并且磁黄铁矿气溶胶的最外层是类似于陨石外表的熔融壳,但是其内部还保持坚硬的棱角状,这些都表明磁黄铁矿在激光剥蚀过程中是熔融行为为主。理解分馏机制之后,合理设置仪器参数,实现了硫同位素的单点微区分析,并且首次实现硫同位素的面分析。赤铁矿的U-Pb定年可以为铁氧化物型铜金铀矿形成时间,甚至成因机制提供有效的制约。但是其应用受到了标样的限制,目前并无合适的基体匹配标样。为了解决该问题本次研究采用了溶液激光联用法进行赤铁矿U-Pb年代学校正。标样为已知U-Pb比值和Pb同位素的混合标样(溶解在2%的硝酸中),配合一块人工合成的赤铁矿晶体;分析样品时同时引入2%硝酸来匹配基体。该方法的优势在于标样绝对均一,而且可根据样品中U-Pb含量进行调整,使得样品和标样的信号值保持相似,可以实现超低含量U的赤铁矿定年。尽管看起来这种方法实现了基体匹配实际分析中还是存在downhole分馏,未来可采取线扫方法尽量降低这种效应。赤铁矿U-Pb年龄显示奥林匹克坝铁氧化物铜金铀矿成矿年代在1.60Ga左右,这和区内的大火成岩省年代一致。微区磷灰石Sr同位素及微量元素表明,长江中下游九瑞矿集区含矿与不含矿的花岗闪长岩体有显著的差别,成矿岩体的Sr同位素和La/Yb比值特征可能是由于再循环的壳源物质所贡献。城门山铜矿的硫化物微量元素和硫同位素面分析结果表明,城门山铜矿的层状矿体经历了热液叠加作用,而且燕山期的热液叠加重新活化并迁移了成矿元素。
[Abstract]:Abstract: This study mainly introduces the development of laser ablation plasma mass spectrometry, and how to apply these methods to the mineralization process of tracer deposits. According to the limited knowledge of the author, the limitations and scope of application of various methods are simply assessed, including a lot of technical details, such as data processing, instrument settings, etc. The method involved in this article is a new method, the other part is more mature and has been widely adopted by international counterparts. From the perspective of application, these methods seem to be enough, but from the perspective of analysis, the fractionation mechanism of elements or isotopes involved in these processes is not clear. Therefore, in addition to the development of new analytical methods, this study also tries to carry out some research on the mechanism of elements and isotope fractionation in the analysis process. The influence of laser parameters on sulfur isotope analysis is evaluated in detail. Taking pyrite as an example, it is found that sulfur isotopes can produce up to 2 per cent fractionation by using different laser parameters of 193nm ArF excimer laser. In order to understand its fractionation mechanism, the aerosol particles were collected and observed by scanning electron microscope and transmission electron microscope. It was found that pyrite decomposed during the laser ablation process and decomposed into two phases. One is pyrite single crystal, the other is amorphous sulfur. The distribution of sulfur isotopes and trace elements is different between the two phases. The ability of the two substances to be blown to the mass spectrum is different, resulting in a fractionation of sulfur and trace elements. The behavior of pyrite in the laser ablation process is very special, because they can not make pyrite under atmospheric pressure melting, the final erosion is a mixture of aerosol troilite crystal nano ball and amorphous sulfur, and collected pyrrhotite in the aerosol particle size is far greater than the pyrite aerosol particle size, and the outer magnet pyrite aerosol is similar to the appearance of the meteorite melting shell, but also keep its internal hard edges, which show that pyrrhotite in the laser ablation process is mainly melting behavior. After understanding the fractionation mechanism, the instrument parameters are set up reasonably, the single point microanalysis of sulfur isotopes is realized, and the surface analysis of sulfur isotopes is realized for the first time. The U-Pb dating of hematite can be an effective restriction for the formation time of the iron oxide type copper gold uranium ore and even the genetic mechanism. However, its application is limited by the standard sample, and there is no suitable matrix matching standard at present. In order to solve this problem, the solution laser method was used to carry out the U-Pb School of hematite. The standard sample is a mixed standard of known U-Pb ratio and Pb isotope (dissolved in 2% nitric acid), combined with a synthetic hematite crystal. When the sample is analyzed, 2% nitric acid is introduced to match the substrate. The advantage of this method is that the standard sample is absolutely homogeneous, and it can be adjusted according to the content of U-Pb in the sample, so that the signal values of samples and standard samples are similar, and the hematite age with ultra-low U content can be achieved. Although it seems that this method has realized downhole fractionation in the actual analysis of matrix matching, this effect can be reduced as much as possible by line scanning in the future. The U-Pb age of the hematite shows that the age of the ore-forming age of the iron oxide copper gold ore of the Olympic Dam is about 1.60Ga, which is in accordance with the era of the large igneous rock Province in the area. Micro apatite Sr isotope and trace elements show that the middle and lower reaches of Yangtze River Jiujiang Ruichang ore concentration area of ore and ore bearing granodiorite have significant differences in rock, metallogenic rock Sr isotopic and La/Yb ratios may be due to the contribution of crustal material recycling. Sulphide trace element and sulfur isotope element analysis results show that the Chengmenshan copper deposit, layered deposit of Chengmenshan Copper Mine has undergone hydrothermal superimposition, and hydrothermal superimposition in Yanshan period and the migration of ore-forming elements re activation.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P597.3;P612

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