190Pt-4He dating of platinum mineralization in Ural-Alaskan-type complexes in the Kamchatka region: evidence for remobilization of platinum-group elements.

Ural-Alaskan-type zonal mafic–ultramafic complexes are the predominant source of platinum-group minerals (PGM) in alluvial deposits worldwide. Processes responsible for the formation of mm-sized grains of Pt-Fe alloys within these deposits remain a subject of ongoing debate. In this study, the ¹⁹⁰Pt-⁴He dating method is applied to isoferroplatinum from the Ural-Alaskan-type Matysken, Itchayvayam, and Filippa complexes of the Koryak-Kamchatka Platinum Belt in order to determine the timing of Pt mineralization and its relation to the regional and local geologic history of the source rocks. Results of ¹⁹⁰Pt-⁴He dating indicate multistage Pt mineralization, with at least two generations recognized. The first generation (70 ± 2 Ma and 77 ± 2 Ma for the northern and southern parts of the Belt, respectively) is contemporaneous with intra-oceanic arc magmatism, which resulted in the formation of the dunite-clinopyroxenite complexes. The second generation is significantly younger (~ 64 Ma), and reflects a later mineralization or recrystallization event following the termination of active volcanism within the Olyutorsky Arc evolution. [ABSTRACT FROM AUTHOR]