Apatite-rich zones in the Uppermost Upper Zone, Northern Limb, Bushveld Complex: Possible non-conventional source of REE and TiO2

Abstract

The uppermost Upper Zone of the Bushveld Complex is known as a potential host of significant apatite-ilmenite resources. Recent exploration studies have delineated two apatite-rich zones representing a huge potential resource of phosphate. A detailed mineralogical and geochemical study of the two apatite-rich zones is undertaken to demonstrate that in addition to phosphate, apatite and ilmenite could be important saleable by-products for REE and Ti. In the Lower Apatite Zone (LAZ), the average concentrations of apatite, ilmenite, and titano-magnetite are 11%, 6%, and 18%, respectively. Grades of about 30 wt% combined apatite, ilmenite, and titano-magnetite can be recovered from the Upper Apatite Zone (UAZ), of which apatite and granular ilmenite constitute 9 and 10%, respectively. There is an association between diamagnetic (apatite), paramagnetic (mostly silicates and ilmenite), ferromagnetic (titano-magnetite) minerals and, to a lesser extent, sulphides. In addition, the majority of the targeted minerals; apatite, ilmenite, and titano-magnetite are relatively coarse, with a median value ranging between 270 μm and 931 μm. In-situ trace element data obtained on apatite demonstrate an increase in Light Rare Earth Elements (LREE) stratigraphically, grading from an average of 3180 ppm Total Rare Earth Elements (TREE+Y) in the LAZ to an average of 4068 ppm TREE+Y in the UAZ, indicating a sub-economic potential of REE that may be economically viable as by-product to phosphate. Preliminary resource estimations show that ~1,405,560 t and ~1,798,056 t of TREE can be exploited from the LAZ and UAZ, respectively. The discrete ilmenite grains are an attractive additional by-product considering their higher average >50% TiO₂ and lower concentration of impurities such as <1.06% MgO, <1.21% MnO, <0.08% Al₂O₃, <0.02% V₂O₅ and <0.01% Cr₂O₃. These results suggest that apatite-rich layers in mafic layered intrusions are viable prospects for economic extraction of REE in conjunction with titanium as other by-products that can be recovered from phosphate rocks.