South Africa - Inkaba.org

Mineralogical, geochemical and structural characteristics of
quartz-arenites of the middle Witteberg Group (Cape
Supergroup) near Kirkwood, Eastern Cape, South Africa
Wernich C. Olivier 1 , P.W.K. Booth 2 , C.R. Anderson 3
1. Nelson Mandela Metropolitan University, South Africa, wcolie4@gmail.com
2. Nelson Mandela Metropolitan University, South Africa, peter.booth@nmmu.ac.za
3. Nelson Mandela Metropolitan University, South Africa, Callum.anderson@nmmu.ac.za
ABSTRACT
A study of Late Palaeozoic Witteberg Group rocks (Cape Supergroup) near Kirkwood, Eastern Cape was carried
out to determine the viability of extracting silica for solar cell production. Mineralogical, geochemical and
structural analyses of selected outcrops of quartz-arenites showed that source rocks in the study area do not possess
the appropriate chemical attributes to warrant extraction of silica. Despite this finding the study presents valuable
information on strata composition and structural data which are compared and interpreted with known regional
structural patterns of the Cape Fold Belt in the Eastern Cape.
Samples from the Witpoort Formation were analyzed using petrographic light microscopy, scanning electron
microscopy and X-ray fluorescent spectroscopy. Analyses indicate that samples are composed almost entirely of
quartz, with accessory biotite, muscovite, sericite, baryte, apatite, rutile and monazite. Haematite occurs most
frequently along fractures, and is more prevalent in the Rooirand Member than the Perdepoort member, giving the
former a reddish brown colour on outcrop. The presence of chemical impurities is thought to be partly controlled
by the original depositional environment, namely, near-shore and beach environments. However, certain
impurities, especially Fe, were most probably emplaced during episodes of faulting related to the Cape Orogeny.
Rocks in the study area display a range of fold styles, mostly showing northward vergence. Low angle thrust faults
dip south and some thrusts dip north. In general, the orientation of fore-thrusts and folds in the study area indicate a
northward-directed compression event during the Late Palaeozoic. This pattern conforms to the structural
development in other parts of the Cape Fold Belt in the Eastern Cape. The south-dipping normal faults and strikeslip
faults that formed during the Mesozoic break-up of Gondwana transect all other structures in the study area.
KEYWORDS: Cape Fold Belt, deformation, silica.
66