【作者】 要梅娟；

【导师】 刘家军； J.Jugo；

【作者基本信息】 中国地质大学(北京) ， 矿物学、岩石学、矿床学， 2012， 博士

【摘要】 南非Bushveld矿床是世界最大的铂族金属矿床，可分为三个成矿单元：梅林斯基矿层（Merensky Reef）、UG2（Upper Group 2）铬铁矿层和普拉特矿层（Platreef）。本文依托已有的野外资料，通过镜下观察、扫描电镜、电子探针等研究手段对Bushveld杂岩三个单元的金属矿物组成进行了详细研究，并利用LA-ICP-MS对相关矿物中铂族元素：钌（Ru）、铑（Rh）、钯（Pd）、锇（Os）、铱（Ir）、铂（Pt）和金（Au）的赋存状态进行了系统分析。本研究中所用LA-ICP-MS仪器可对样品进行线剥蚀，所得数据用Iolite软件进行处理，最终形成了元素的面扫描图像，这种图像比普通的激光剥蚀束斑分析包含更多的信息，能够获得元素在一个微区域内的总体分布情况，可研究较为复杂的样品，对深刻理解其地质意义很有帮助，可以反映非均质矿物中元素的分布状态及矿物之间边缘带的微量元素分布情况。研究的主要矿物有：黄铁矿、镍黄铁矿、黄铜矿、磁黄铁矿和铬铁矿。分析表明，有2个包体式镍黄铁矿的Ni含量明显高于铬铁矿颗粒外的间隙式镍黄铁矿，分别高出5.851%和7.162%，而相应Fe含量则明显偏低；将Bushveld三个成矿单元及美国Stillwater矿床对比研究发现，镍黄铁矿是Pd的主要载体，Pd、Rh和Ir主要以固溶体形式分布在镍黄铁矿中；黄铁矿是重要的铂族元素载体之一，原生的黄铁矿在与镍黄铁矿共生时富集Os、Ir、Ru和Re，而次生黄铁矿基本不含PGE；磁黄铁矿中PGE含量很低，只有少量样品达到检测线；黄铜矿中主要含少量的Pd和Rh。Pt主要伴随着Bi主以铂族元素矿物的形式分布在硫化物之间或者硅酸盐基质中；UG2铬铁矿层的铬铁矿中没有达到检测线的以固溶体形式存在的铂族元素。铂族元素的LA-ICP-MS的分析结果也显示不同产出形式的硫化物中铂族元素的浓度存在差异，认为是由于UG2铬铁矿层经历了后期的岩浆或热液流体的改造所引起。UG2铬铁矿层的硅酸盐进行电子探针分析发现，铬铁矿包体中角闪石的Mg和长石中的Na含量明显高于基质中的角闪石和长石。更多还原

【Abstract】 The Bushveld Complex （South Afica） is the largest known layered intrusion on Earth,contains approximately 80% of the world’s resource of platinum group element （PGE）.The PGE mineralization mainly occurs as three units: the Merensky reef, Platreef andUG2 chromitite. In this paper, we investigated the distribution of PGE amongchromite, the trapped sulfide inclusions within chomite, and the sulfides interstitial tochromite from the Bushveld Complex. Samples were analyzed with scanning electronmicroscopy （SEM） and EPMA （Electron probe micro-analyzer） to select small areas,and keep a record of the assemblages prior to ablation. The mode of our plasma-massspectrum （LA-ICP-MS） analysis uses scanning ablation and the Iolite software wasused to combine parallel adjacent line-scan into coherent element images. Advancesin the LA-ICP-MS analysis have allowed us to obtain high resolution trace elementmaps of small features, especially for the sulfide inclusion. Comparison of the imageswith the traditional spot analysis, the images can obtain more comprehensiveunderstanding of overall distribution of elements in the complex chromitite samples.The EPMA data of sulfide show that the pentlandite enclosed in the chromite hashigher Ni than the interstitial ones, which suggest that they are modified by the latemagmatic and/or hydrothermal melt/fluids. We found out that the primary pyriteassociation with penlandite takes Os, Ir, Ru and Re; Rhodium is not uniform amongdifferent grains within the same sample; platinum and Bi concentrated outside thesulfides, nothing inside. Chromite from the UG2 chromitite has no detectable HSE insolid solution; pentlandite is the main host of Pd.Inclusions in earliest crystallizing silicate minerals are indicative of a very early-stagesulfide liquid in the system, as they will have cooled and fractionated within anessentially closed system.The comparison of the PGE distributions between theinterstitial sulfide and sulfide inclusions in the same sample provide extremely usefulinformation to understand how PGE were incorporated, how much is from melt andhow much is hydrothermal. EPMA data shows the hornblende in the inclusions ischaracterized by high Mg, and the plagioclase in the inclusions is distinctly more salicthan that in the outside with An6to An21in the inclusions and the outside is An₅₆toAn₇₃.更多还原