The age of the Marble Hall diorite, its relationship to the Uitkomst Complex, and evidence for a new magma type associated with the Bushveld igneous event

Abstract

Mesocratic to leucocratic diorite intruded as sills in the deformed Marble Hall Fragment in the vicinity of Marble Hall, Mpumalanga Province, South Africa. A mesocratic variety gives a 207Pb/206Pb SHRIMP age on zircon of 2055.6 ±3.1 Ma. This age similar to that of the Bushveld Complex and the conduit-like Uitkomst Complex. Because the more primitive variety of Marble Hall diorite is chemically comparable with the chill-zone rocks of the Basal Gabbro of the Uitkomst Complex, a new magma type (Bu-type magma), associated with the Bushveld igneous event, at c. 2056 Ma, is postulated. The emplacement of this magma preceded the emplacement of the Bushveld B 1-type magma, and may also be parental or genetically related to the Lindequesdrift intrusion (in Malmani dolomite), the Roodekraal Complex, and the Rietfontein Complex in the Potchefstroom area. These findings reinstate the economic potential of all these sub-Rusteriburg Layered Suite intrusives.