Oxide minerals in the Liqhobong kimberlite, Lesotho

The oxide minerals in kimberlite from Liqhobong, Lesotho, are represented by discrete ilmenite nodules, groundmass ilmenite, spinel solid solutions, and perovskite. The discrete ilmenite nodules have margins that are enriched in Mg (15–21 weight percent MgO) relative to the cores (11–13 weight percent MgO). The Mg enrichment is restricted to the outermost margins of the nodules (300–500 μm) and is believed to be of metasomatic origin. The groundmass ilmenite has a Mg content similar to that of the margins of the discrete ilmenite nodules but is more enriched in Fe₂O₃. Spinels are represented by two distinct varieties: a ti-tanian–ferrian pleonaste that belongs to the Mg₂TiO₄–Fe₂TiO₄–FeAl₂O₄–MgAl₂O₄ solid solution series and trends in composition toward MgFe₂0₄ and Fe₃0₄, and a titanian aluminous chromite that belongs to the FeCr₂O₄–MgCr₂O₄–FeAl₂O₄–MgAl₂O₄ solid solution series. The titanian aluminous chromite apparently crystallized as a liquidus phase prior to the crystallization of titanian pleonaste from the late-stage Ti-rich fluids that reacted with the ilmenite nodules. The perovskite is Nb-bearing and is rich in rare-earth elements (4.8–6.1 weight percent REE oxides). It is enriched in light REE relative to heavy REE. The enrichment of perovskite in REE may be related to partitioning of these elements between perovskite and an immiscible carbonate liquid or to equilibration of perovskite with a CO₂-rich fluid enriched in light REE.