Petrogenesis of Ferroszaibélyite and Ekaterinite in Kimberlites: Influence of Volatile Composition, Fluid Regime, and Redox Conditions

A direct correlation between the B content and the composition of a volatile phase, which is responsible for metasomatic alteration of kimberlites, is established. The enrichment of underground brines in boron should therefore be attributed to its deep-seated sources. Magnesium and Fe necessary for the formation of ferroszaibélyite were mobilized from pore solutions of cooling serpentine, which becomes almost purely magnesian at a decreasing temperature. Ekaterinite formed in different (oxidizing) conditions compared to ferroszaibélyite as is evident from inclusions of Fe oxides and hydroxides in the mineral.