Can we use mantle normalization and metal ratios for identification of PGE sources in metal-rich black shales?

摘要

ft has been shown that Ni/Cu versus Pd/Ir and Cu/Ir versus Ni/Pd ratios, as well as mantle normalized metal patterns, can be successfully used for the evaluation of the effects of partial melting, crystal fractionation and sulfide saturation in mafic and ultramafic rocks (Barnes et al. 1987). PGEs enrichments have been recently found in Zn-, Cu-, and Ni-rich black shales in a number of geological settings. These facies are generally associated with the development of continental rift structures, both without significant volcanic activity (examples in Canada, China, Finland and Poland) and with volcanic activity (Czech Republic and Namibia). In these PGE-metal-rich black shales the fractionation of the PGE in the black shales reflects the fractionation of the PGE in the associated volcanic rocks. It was further concluded that, in metal-rich black shales in which distributions of Ni and Cu have been altered by various processes, the Ni/Cu versus Pd/Ir and Cu/Ir versus Ni/Pd ratios plots are applicable for determination of the source of PGEs only after careful evaluation of Ni and Cu enrichments.