The Geology and Geochemistry of the Sterkspruit Intrusion, Barberton Mountain Land, Mpumalanga Province
THE GEOLOGY AND GEOCHEMISTRY OF THE STERKSPRUIT INTRUSION, BARBERTON MOUNTAIN LAND, MPUMALANGA PROVINCE Gavin Patrick Conway A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 1997 11 DECLARATION I declare that this dissertation is my own, unaided work. It is being submitted for the Degree of Master of Science in the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination in any other University. __I_It __ ·daYOf A~V\.-~t 19 't1-- 111 ABSTRACT The Sterkspruit Intrusion, in the south-western portion of the Barberton greenstone belt, is a sill-like body containing rocks of gabbroic to dioritic composition. It is hosted by a sequence of komatiitic basalts and komatiites of the Lower Onverwacht Group. The intrusion is considered unique in this area in that it lacks ultramafic components and has no affinities with the surrounding mafic- to- ultramafic lavas. The gabbroic suite also contains an unusual abundance of quartz, and the chill margin shows an evolved quartz-normative, tholeiitic parental magma. Based on petrographic and geochemical evidence, the intrusion can be subdivided into four gabbroic zones and a quartz diorite, which is an end product of a differentiating magma. The chill margin records an MgO content of 4.8%, an Mg# of 42, an Si02 value of 52.5% and a normative plagioclase composition of An 44. The sill-like nature of the body, indicated by geochemical trends, and the steep sub-vertical layering, point to a body that has been tilted along with the surrounding lavas.
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