布什维尔德铂族元素矿床:铂族矿物赋存状态及其成因  

PGE deposits in Bushveld Complex:The occurrence and origin of the platinum-group minerals

作　　者：谭娟娟[1,2] 朱永峰[1,2] 

机构地区：[1]造山带与地壳演化教育部重点实验室 [2]北京大学地球与空间科学学院,北京100871

出　　处：《地学前缘》2009年第2期227-238,共12页Earth Science Frontiers

基　　金：国家自然科学基金创新群体项目(40821002);国家科技支撑计划重点项目(2006BAB07B08)

摘　　要：总结南非布什维尔德杂岩体中Merensky Reef(简称MR矿层)和Platreef(简称PR接触带)两类铂族元素矿床的矿床地质、矿化特征以及铂族元素的赋存状态。MR矿床是典型的层状铂族元素(PGE)矿床,在杂岩体东部和西部发育,PGE总含量稳定,赋存在堆晶间隙硫化物中,常以PGE硫化物的形式产出。PR接触带型矿化集中在杂岩体北段,整体上不连续,各个矿床的具体特征由于底盘岩性的多变而不同,PGE主要赋存在碲化物和砷化物等半金属化合物中,可以脱离硫化物产在硅酸盐矿物中。相关的实验研究显示,PGE在岩浆结晶过程中发生分异,Pd/Ir比值体现了硫化物的分异程度;Pd比Pt更容易被氧化以及在热液中迁移,Pt/Pd比值体现了混染和热液的作用,这些因素造成了PR接触带与MR矿层中PGE赋存状态的差异。岩浆可能在侵入之前已经达到了硫饱和,岩浆房的压力变化和岩浆通道对于PGE的富集有重要意义,热液流体可以对已经形成的PGE矿化进行改造。Geology and mineralogy of two types of platinum-group elements （PGE） mineralization in Bushveld Complex have been summarized, with special attention to the occurrence of the PGE-bearing minerals. Hosting three quarters of the known PGE resources on Earth, Bushveld Complex is the largest repository of PGE in the world, having intruded the Kaapvaal craton in the Paleoproterozoic. The east and west limbs of the Complex are characterized by homogeneous layered mineralization, represented by Merensky Reef （MR）, in which the PGE content is averagely continuous. Most PGE concentrates in the intercumulus PGE-sulfide. In the north limb, however, the PGE mineralization developing in contact zone is referred to Platreef （PR）. The mineralization is discontinuous, and the characteristics of different deposits vary along the trend with the changes in footwall lithology. The PGE carriers are dominantly semimetal compounds such as arsenide, telluride and antimonide. In such case, PGE can be decoupled from sulfide and occurred in silicate minerals. Related experiments demonstrated that PGE would fractionate during magma crystallization, and the effect of sulfur in this process could be represented by Pt/Pd ratios. Pd is more vulnerable to oxidation and more likely to remobilize with hydrothermal fluids as shown by Pt/Ir ratios. Those factors have caused the differences of the PGE occurrences in Platreef and Merensky Reef. The magma could have reached sulfur-oversaturation before emplacement; the change of pressure in magma chamber and the magma conduits played important roles in PGE concentration and deposition. Fluid may have modified the existed PGE assemblage.

关 键 词：铂族元素 布什维尔德杂岩 层状侵入体 接触带型矿化 

分 类 号：P571[天文地球—矿物学]