The bushveld granites and associated rocks in the area north-west of Warmbaths, Transvaal

Abstract

From mapping and subsequent petrological and chemical investigation the existence of two separate phases of granitic rocks of the Bushveld Complex in the Warmbaths area was established; viz: (i) the Baviaansberg granite suite and (ii) the Verongelukspniit granophyre suite. Field relationships indicate a definite age-difference between the two granitic phases. The older Verongelukspruit granophyre suite is represented by a series of rocks ranging from granite porphyry through porphyritic microgranophyre and porphyritic granophyre to granophyre. The younger Baviaansberg granite suite essentially consists of coarse-grained main facies, which shows some textural variations, and a fine-grained contact facies. A comparison between the granitic rocks of the Warmbaths area and those at Zaaiplaats indicates many similarities and a tentative correlation is given. The older Verongelukspruit granophyre suite is considered to represent the first phase of granitic intrusion of the Bushveld Complex. The petrological characteristics of this rock suite indicate that it owes its present character to metamorphic recrystallization. This metamorphism is considered to be the result of the intrusive activity of the younger, main phase of granitic intrusion viz. that of the Baviaansberg granite suite. The Rooiberg felsite attains a thickness of 3000 m and is subdivided into two units: (i) the upper felsite unit, and (ii) the lower felsite unit. The lower unit consists of various types of felsite whereas the upper unit also includes a volcanic breccia, tuff and an ash-flow tuff. The recognition of a twofold subdivision in the Rooiberg felsite and the mapping of the separate units has greatly aided in unravelling the structure of the area, which indicates that two major periods of deformation dominated the structural evolution of the area viz. (i) a pre- and early-Waterberg period of deformation, and (ii) a post- and possibly syn-Waterberg period of deformation.