A major swarm of 'lamprophyric' dykes exposed in platinum mines of the Bushveld Complex, South Africa: geochronology, petrology and mineral chemistry

摘要

Here we document a major swarm of 'lamprophyric' dykes cross-cutting portions of the 2.06 Ga Bushveld Complex. The dykes are mostly blind at surface but exposed by underground platinum mining operations in the Rustenburg Layered Suite of the Bushveld Complex, providing a unique subsurface insight into the magnitude of the swarm. The dykes predominantly strike WNW-ESE and fall along subparallel anastomosing sets in plan view. Most dykes range from 0.5 to 2 m in true width, sometimes with millimetre-scale veinlets as off-shooting networks. The dykes bifurcate and anastomose at various scales in plan view. All dykes are vertical/subvertical and the margins may be chilled, often foliated, with lineations defined by alignment of mica crystals. Abrupt changes in mineral abundance are often recognisable as bands across a single dyke, demonstrating their compound nature. Dykes can appear 'stepped' in cross-section, sometimes with accumulations of olivine macrocrysts and/or crus-tal xenoliths located within these steps (typically of Transvaal Supergroup sediments and Bushveld lithologies).