REE Mineralization of the Blockspruit Fluorite Prospect, Bushveld Granitic Complex, South Africa: Geochemical, Mineralogical and Fluid Inclusion Studies

The Blockspruit REE prospect in northwestern Pretoria, South Africa, is hosted by the Bushveld complex. HREE-rich ferro-edenite rocks intrude into the Kenkelbos-type granite, which is present in the fluorite prospect. We carried out geochemical and mineralogical studies of samples collected from 9 drill holes. Three types of REE ores have been identified in the Blockspruit prospect: (1) weathered crust near surface (30-50 m) with residual monazite and xenotime, (2) altered ferroactinolite rocks including REE-poor apatite replaced by monazite and xenotime near surface and (3) primary ferro-edenite rocks including REE-rich apatite (with up to 20.3 wt% ƩREE2O3, 9.36 wt%ƩHREE2O3) from the deep zone. Fluid inclusions and C-O-H isotopic studies suggested that these ores formed by during a continuous process. A complex fluid (F-Cl-FeCa-Na-K-CO2-CH4) released from the ferro-edenite by hydrothermal alteration formed ferro-actinolite and REE-poor apatite replaced by monazite and xenotime. With further alteration, the REE-poor apatite, including the REE phosphate minerals, decomposed, with only monazite and xenotime remaining in the weathered crust. Therefore, REE mineralizations in the Blockspruit prospect are related to both of magmatic and hydrothermal processes.