Abstract
M.Sc. (Geology)
The Main Reef Complex (MRC) section is developed in the Zwartkoppie
and Sheba Formations of the Onverwacht and Fig Tree Group
respectively.
The section is represented by three shear zones, associated with
a prominent anticlinal structure, locally known as the Birthday
No.2 anticline.
This tight isoclinal structure is marked by a chert unit, with a
core of green quartz-carbonate schist, and is overlain and surrounded
by greywackes and shales of the Sheba Formation.
At depth the main mineralized fracture occurs to the south of,
and parallel to the Birthday No.2 chert bar. Above the crest of
the anticlinal structure gold mineralization is associated with
three shear zones (which transgress the bedding of the greywackes
and shales) known as the No .. I, No. 2 and No. 3 Fractures.
Pyrite and arsenopyrite are the main ore minerals, with minor
amounts of chalcopyrite, sphalerite, tetrahedrite and pyrrhotite.
Pyrite mineralization is ubiquitously developed along the shear
zones, while arsenopyrite mineralization is restricted to certain
areas. Assay data of the greywackes and shales show that there is
a correlation between gold contents and the abundance of arsenopyrite.
Gold has been observed in association with all the sulphide
minerals present, and as inclusions within pyrite and
arsenopyrite. Electron microprobe analyses have revealed significant
levels of gold in arsenopyrite, probably as submicroscopic
inclusions.