Mineralogical-Geochemical Types and ~(190)Pt-~4He Age of Ferroan Platinum of Placers of the Anabar River Basin, Northeastern Part of the Siberian Platform

摘要

Typical features of platinum group minerals (PGMs) and the results of Pt-190-He-4 dating of the Fe-Pt solid solutions are presented for complex gold-platinum-diamond placers with unidentified sources of the Anabar River basin. For the first time, the Pt-190-He-4 isotopic system is used for determination of the possible age of the primary source of a PGM placer from the example of ferroan platinum with a disordered structure along with isoferroan platinum. The PGMs of these placers mostly include ferroan platinum and isoferroan platinum and rare Ru-Ir-Os alloys. The calculated bulk composition of the silicate inclusion of Ir platinum corresponds to the rocks of the ijolite-melteigite series. The Pt-190-He-4 age of the Fe-Pt solid solution grains is 261 +/- 13 Ma. Thus, our data indicate the relation between placer PGMs of the Anabar River basin and Permian-Triassic complexes of alkaline-ultramafic rocks.