In search for primary sources of placer diamonds of northeast Siberian craton: Evidence from the U-Pb ages and geochemistry of alluvial zircons

The northeastern Siberian craton stores numerous placers of diamonds that differ in morphology and texture, and originate from different types of primary deposits, primarily kimberlites. Analyses of mantle zircons selected from samples of alluvial and coarse clastic sediments in the watersheds of the Olenek and Kyutyungde rivers in the Anabar-Olenek subprovince of the Yakutian diamond province provide constraints on kimberlite magmatism events in the area. The new U-Pb ages and typical kimberlitic signatures of the Kyutyungde zircons trace-element patterns reveal three main magmatic events that produced kimberlites: Middle Paleozoic (Late Devonian to Early Carboniferous), Jurassic and Triassic. The Jurassic zircons (177-149 Ma) are mainly related to kimberlites in the proximal Kuoika-Molodo and Khorbusuon fields. Triassic zircons (240-221 Ma) were probably released during large-scale erosion of the eastern Anabar shield, however, the presence of such zircons in the Kyutyungde area indicates that kimberlites of the respective magmatic stage may exist within the immediate vicinity of the area. The only Middle Paleozoic zircon sample (358.6 Ma, D-3-C-1 boundary) may originate from a proximal kimberlite within the Kyutyungde area. The presence of Middle Paleozoic kimberlitic zircons, along with harzburgite-dunitic pyropes, indicates that the primary deposit of diamonds and related minerals may exist near or within the Kyutyungde area. Late Ediacaran-Early Cambrian (573-473 Ma) mantle zircons found in Early Cambrian conglomerates of the area, along with other mantle minerals including Cr spinel of a diamond assemblage, record another Precambrian event of potentially diamondiferous magmatism in the Kyutyungde basin.