The Na-Mg-Fe-Ti Oxide Mineral in Association with Picroilmenite and Freudenbergite from Kimberlite of the AK8 Pipe, Botswana (Natural and Experimental Data)

摘要

The previously unknown Na-Mg-Fe-Ti oxide mineral of the idealized composition Na-4MgFe_2~(3+)Ti_5O_16 was discovered in altered areas of picroilmenite ((Fe, Mg)TiO_3) xenocrysts in association with freudenbergite (Na_2(Ti, Fe)_8O_(16))) in porphyric kimberlite of the AK8 pipe in the Orapa kimberlite field (Botswana). According to the classification of a South African geologists, the AK8 pipe is composed of kimberlite of group I. This rock consists of serpentinized olivine phenocrysts, rarely phlogopite and picroilmenite, as well as chrome-diopside and garnet cemented by fine-granular carbonate-serpentine aggregate with micro-grains of ore minerals. Secondary mineralization of the metasomatic type represented by freudenbergite and Na-Mg-Fe-Ti oxide is observed in fractures and rims on picroilmenite xenocrysts from the AK8 pipe.