A New Occurrence of Merensky Reef on the Flanks of the Zaaikloof Dome, Northeastern Bushveld Complex: Relationship between Diapirism and Magma Replenishment

摘要

Exploration for platinum-group elements has resulted in the discovery of an occurrence of Merensky reef in the eastern limb of the Bushveld Complex, South Africa. The new discovery was made on the Dwarsrand property in the poorly known boundary area between the intensively explored western and central sectors of the eastern limb. This boundary area is largely composed of domes and basins that may, in part, be aligned along a regional lineament, the Wonderkop fault. Transvaal Supergroup metasediments in the core parts of the domes form prominent hills, whereas the Bushveld Complex in the intervening basins is restricted to areas of poor outcrop. The formation of domes is attributed to diapirism triggered by gravitational loading and heating of the Transvaal Supergroup in response to intrusion of the Bushveld Complex. Merensky reef was located beneath cover rocks in an area where the Critical and Main zones are uplifted and attenuated against the southern flank of the Zaaikloof dome. Drill holes, although collared in Upper zone, intersected the Critical and Main zones at relatively shallow depths. As a result of the uplift, the Critical and Main zones, including the Merensky reef, are steeply dipping. The base of the Upper zone forms an intrusive unconformity and the layering in this zone has a much shallower dip. Economically significant grades were obtained on the Dwarsrand property, but exploration was terminated because of poor strike continuity.