Investigation of three Fe-Ti oxide deposits associated with Grenvillian anorthosite massifs as potential source for lunar analogue ilmenite

Terrestrial ilmenite has been assessed for its suitability in the preparation of a simulant of lunar high-Ti mare regolith, which is needed to test oxygen production on the lunar surface during future missions. Petrographic observations using optical and electron microscopes revealed that ilmenite grains in the Mirepoix, Sanford Lake, and Degrosbois Fe-Ti oxide deposits from Grenvillian anorthosite massifs contain hercynite in their rims but that hematite exsolution is absent in three of eight studied samples. Electron microprobe analyses showed that the ilmenite grains vary in TiO2 from 38.82 to 52.34 wt.%; in FeO from 33.15 to 45.88 wt.%; in Fe2O3 (calculated from stoichiometry) from 2.18 to 27.03 wt.%; in MgO from 0.05 to 2.49 wt.%; and in MnO from 0.26 to 1.51 wt.% and are thus comparable in composition to lunar ilmenite. Ilmenite, free of hematite, in two samples was homogeneous in composition (e. g., sample SL1: 50.4 -51.4 wt.% TiO2). Two sub-solidus reactions occurred amongst the oxide minerals in the studied deposits: (i) exsolution of hercynite in magnetite; and (ii) reaction between the hematite component in the ilmenite and the ulvospinel component of the magnetite, forming new ilmenite, which includes the hercynite. The reaction between the hematite component in the ilmenite and the ulvospinel component of the magnetite, when conditions are favorable for diffusion, produces ilmenite grains that are homogenous in composition and free of hematite exsolution. Ilmenite with little or no Fe3+ may occur in massive, fine-grained, and metamorphosed Fe-Ti oxide deposits and provide a terrestrial analogue source of ilmenite useful for the production of lunar mare simulant.