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

Abstract:

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.

Key words: Platinumgroup elements; Bushveld Complex; layered intrusion; contactstyle mineralization