Average contents of platinum group metals in ultramafites

摘要

Assessment of contents of the platinumgroup metals(PGM) and gold was carried out for olcanic(komatiites, kimberlites, meimechites) and plutonicultramafites of zonal, layered and ophyolitic massifs(harzburgites, dunites, orthopyroxenites,clinopyroxenites). Obtained results show that twovarieties of rocks can be distinguished by the PGMconcentration level:one with the lower content (10-30ppb, an average of 20 ppb)-komatiites and kimberlites;the second branch with the higher PGM content(30-80ppb, and average about 50 ppb)-dunites, pyroxenites,harzburgites. Diagrams of normalized-to-chondriteratios display two main types of the PGM distribution.The first group (komatiies, kimberlites) demonstratesthe weakly differentiated distribution of PGMbehaviour with a raised content of light PGM(Ru,Rh,Pd)and reduced content of the heavy ones (Os,Ir,Pt). Thesecond group (for example, dunites andclinopyroxenites of layered massifs) has the sharplydifferentiated distribution of PGM and the raisedcontent of Pt and Pd. And if komatiies and kimberlites(the first type) are really forming as the result ofa spacious anatexis, so their enrichment in light PGMought to carry out enrichment of restites in heavy platinoids.