PGE mineralization in the Zhubu mafic intrusion: implications for the origin of the reef-type PGE deposits

摘要

The origin of reef-type PGE deposits remains controversial (Maier, 2005). For example, the Merensky Reef of the Bushveld, there are two kinds of models to explain its formation. The first is that the PGE are mainly concentrated by primary magmatic sulfides by many researchers (Barnes and Maier, 2002; Cawthorn and Boerst, 2006; Cawthorn et al., 2002; Viljoen, 1999); the second is PGE could have been precipitated from late magmatic or hydrothermal fluid (Boudreau, 2008; Boudreau and Meurer, 1999; Willmore et al., 2000). The first model is also called "top-loaded", it has no explanations about the role played by the volatiles in the ore formations (Boudreau, 2008); the second is also called "bottom-loaded". However, this model is not consistent with the observations that there is no evidence of PGE depletion below the reefs whereas the rocks above the reefs tend to be highly depleted in PGE (Barnes and Maier, 1999). Therefore, new model is needed to explain all the controversies.