Ilmenite-Apatite Enrichments in the Upper Zone of the Bushveld Complex: A Major Titanium-Rock Phosphate Resource

Detailed modal analyses of apatite-enriched layers in the upper 1000 m of cumulates of the Upper Zone have shown them to contain appreciable quantities of granular ilmenite. This greatly enhances the economic significance of these layers as a potential resource of combined apatite and ilmenite. The mineralized layers encountered in the very limited number of borehole intersections through the uppermost 1000 m of the Upper Zone suggest a widespread development of two mineralized zones. A lower zone is approximately 30 m thick with a combined apatite and ilmenite content of slightly more than 20 vol%, of which granular ilmenite constitutes between 4 and 6 vol%. The upper mineralized zone is up to 40 m thick, with an apatite plus ilmenite content of between 18 and 20 vol% and a granular ilmenite component of approx-imately 10 vol%.

Textural and compositional relations suggest the periodic development of an immiscible Fe-Ti-Ca-O-P liquid during fractional crystallization of the topmost 1000 m of the Upper Zone. The development of the mineralized zones at the base of distinct geochemical cycles suggests that formation of the immiscible FeTi oxide-apatite melts was brought about by magma mixing processes. The tremendous strike extent of the Upper Zone, in excess of 400 km, implies that this zone has the potential of hosting major combined rock phosphate-titanium deposits, with a resource potential of several billion tons of ore grading about 20 vol% combined ilmenite and apatite.