Abstract

Electron microprobe analyses reveal a wider range of ilmenite compositions than previously reported from carbonatites, as solid solutions in FeTiO 3 -MgTiO 3 -MnTiO 3 -Fe 2 O 3 , with high-Nb ilmenites containing up to 3.68 wt.% (Nb 2 O 5 + Ta 2 O 5 ). Coexisting magnetite and ilmenite (with low MgO and MnO) from the reaction rocks give equilibration temperatures of 570-595 degrees C and oxygen fugacities of 10 (super -18.5) to 10 (super NG19.5) atmospheres. The ilmenites are distinguished from ilmenites in kimberlites by high MnO, very low Cr 2 O 3 , and high (Nb 2 O 5 + Ta 2 O 5 ).Modified journal abstract.

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