The geology of the acid phase of the Bushveld complex, north of Pretoria: a geochemical/statistical approach
A petrographical and geochemical study of the acid phase of the Bushveld Complex, north of Pretoria, was undertaken with the aim to identify the different rock units, to determine their interrelationships and to classify the rocks as well as describing their geochemistry. The oldest geological formation in the area is the Rooiberg Group which is subdivided into two units, namely the Kwaggasnek (lower) and Schrikkloof (upper) Formations. Petrographical, mineralogical and geochemical data are submitted for the different units. From the data it can be deduced that these units formed as products of a single parental magma, while statistical manipulation of the geochemical data indicates that these formations differ significantly from the Damwal Formation farther to the east. The gradational contact relationships between the felsites and underlying granophyre are described and explained in the text. The various granophyre occurrences of .the Rashoop Granophyre Suite are classifiedand described. The mineralogical, petrographical and geochemical data indicate a limited differentiation trend from the felsites into the granophyre. This may indicate that the granophyre in part resulted from . the rapid crystallization of the parental magma of the Rooiberg Group. A model for the origin and formation of the Rashoop Granophyre Suite, based on petrographical and-qeochernical evidence, is proposed. The granites are subdivided according to age and field relationships, as well as mineralogical, petrographical and geochemical characteristics into the Sekhukhuni, Verena, Makhutso, Klipvoor and Klipkloof granites. The mode of intrusion as well as the mineralogical, petrological and geochemical composition of each type are discussed. A petrochemical investigation of the granites indicate that the various granites, with the exception of the Klipkloof granite, represent the differentiation products of a single parental magma. A similar study on the Makhutso and.Verena granites indicates that leptite assimilation influenced the final differentiation trend in these granites, causing enrichment in certain elements and depletion in others.