ON THE GEOLOGY OF THE ALKALI ROCKS IN 

 THE TRANSVAAL 



H. A. BROUWER 



Delft, Holland 



CONTENTS 

 Introduction 



Igneous Complex of the Bushveld 



Place of the Main Transvaal Laccolith 



Bottom of the Laccolith 



Roof of the Laccolith 



Accompanying Dikes and Intrusive Sheets 



Tectonic Changes Connected with the Intrusion 



Contact Metamorphism 



Rock Types of the Bushveld Complex 



Pneumatolysis 

 The Occurrences of Alkali Rocks 



a) The Pilandsberg 



General Character of Rocks 



The Rocks of the Country around the Pilandsberg 



Dike Rocks 



Pegmatites 



Mechanism of Intrusion of the Pilandsberg Complex 



Age of the Pilandsberg Complex 



b) Other Occurrences of Nepheline Syenites and Allied Rocks 



The Intrusion on Leeuwfontein (320) 



Nepheline Syenite Region to the West of Lydenburg 



c) Origin and Age of the Nepheline Syenites and Allied Rocks 



INTRODUCTION 



In June 19 10 I studied the geology of the occurrences of nephe- 

 line syenites in the Transvaal, and the results were published in the 

 same year in a paper, "Oorsprong en Samenstelling der Trans- 

 vaalsche Nepheliensyenieten," which contains a contribution to the 

 geology and a petrographical description of the nepheline syenites 

 and various allied rocks. In the following pages some geological 

 questions will be treated more in detail and the main results of 

 recent work of the Geological Survey of South Africa are added. 



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