Discovery and resource evaluation of the Lesego Platinum Merensky Reef and UG2 Chromitite hosted platinum group metals deposit adjacent to the Phosiri dome and the associated effects of Phosiri dome on the reef horizons, bushveld complex, South Africa

Abstract

The recently discovered Lesego Platinum Merensky Reef and UG2 Chromitite deposit is a 39 millionounce PGE deposit hosted in the northeastern portion of the Bushveld Complex, South Africa. The upward displacement of floor rock during the emplacement of the Rustenburg Layered Suite of the Bushveld Complex as a result of gravitational forces has resulted in the economically important horizons, which would normally be at several kilometers depth, being brought closer to surface by the Phosiri Dome. The Phosiri Dome has, however, had a dramatic effect on the morphology and grade of the Merensky and UG2 reefs. The reefs are almost vertical in close proximity to the Phosiri Dome, but rapidly flatten out at depth to the shallow westerly dips more consistent with traditional Merensky and UG2 reefs in the area. A gabbro contaminated with anatectic melt appears to have obliterated the reef horizons closer to surface, resulting in the upper orebody remaining undiscovered since the area was first explored in the 1980’s. Reef morphology and PGE mineralogy in the Merensky Reef further away from the Phosiri Dome are consistent with that of surrounding deposits.