PLATINUM-BEARING PLACERS: MINERAL ASSOCIATIONS AND THEIR ¹⁹⁰Pt-⁴He AND Re-Os AGES, AND POTENTIAL LINKS WITH LARGE IGNEOUS PROVINCES IN THE SIBERIAN CRATON

Placer deposits in the Siberian platform are closely associated with well-known platiniferous intrusions (Kondyor, Inagli, Noril'sk, Chiney, and Guli) but there are also abundant platinum-group mineral (PGM) placers of large areal extent in the river basins of Siberia (Vilyui, Lena, Aldan, Anabar, and Olenek) for which the primary sources are unknown. The Pt-1(90)-He-4 dating method is introduced, compared with existing Re-Os isotope dating of PGMs, and applied to Pt-bearing placers of Siberia. Correlations between the Pt-190-He-4 and Re-Os isotope ages of the PGMs and with ages of major magmatic events in the Siberian craton show that the potential sources for some of the placers are likely buried Precambrian mafic-ultramafic intrusions of Large Igneous Provinces (LIP). The approach of this paper can be applied to other cratonic areas with alluvial PGMs of unknown origin.