gems, diamond, Russia, Yakutia, inclusions, large diamonds, garnet

Large diamonds (10–200 carats) from the Udachnaya, Mir, and Aikhal kimberlite pipes of Yakutia contain mineral inclusions similar to those found in smaller diamonds. Most of these inclusions, particularly from the outer portions of the diamonds, are garnets of harzburgitic paragenesis, with fewer belonging to lherzolitic and eclogitic groups, along with some chromite diamond inclusions (DIs). A distinctive feature of the harzburgitic and some lherzolitic garnets is their sinusoidal rare-earth element (REE) patterns, in contrast to the normal light REE-depleted patterns seen in eclogitic garnets. These sinusoidal REE patterns suggest a complex petrogenetic history for the garnets, involving initial partial melting followed by metasomatic enrichment—especially of light and middle REEs—by fluids likely rich in C-O-H-N-S rather than carbonatitic compositions, as evidenced by negative Ba and Sr anomalies. These findings challenge the widely held assumption that most DIs are syngenetic with their host diamonds. Instead, the preserved geochemical signatures in harzburgitic garnet DIs reveal a history that predates diamond encapsulation, providing strong evidence that these inclusions are protogenetic rather than syngenetic.