Mining in focus
Glacier theory
According to Professor McCarthy, a strange rock type is
associated with all the goldfields in the Witwatersrand Basin,
referred to by most geologists as ‘puddingstone’.
Puddingstone is basically an unsorted conglomeration of
rocks that consists of distinctly rounded pebbles whose colours
contrast sharply with the colour of the much finer-grained,
often muddy matrix or cement surrounding them. The size of
the pebbles in the puddingstone found in the Witwatersrand
Basin varies considerably, and they are of diverse types. “It is an
accepted geological fact that in most other parts of the world,
‘puddingstone’ (correctly known as tillite) is deposited by ice,” says
Professor McCarthy.
“The idea of glacial transportation of material in the
Witwatersrand Basin was first proposed in the 1950s by Dr
J H Wiebols, a Union Corporation geologist, and was
then, without reason, abandoned, and it never gained
traction again. We came across it while working on
the Evander Goldfield, trying to understand how its
gold-bearing reef was deposited. We continued
running into these puddingstone rocks and I
vaguely remembered this weird theory about
the glacial origin of the Witwatersrand
conglomerates. We had access to, and
read, many excellent internal company
reports about the Evander Goldfields,
as well as Wiebols’s articles. From
those reports it was clear that
the only way those rocks could
have originated was by glacial
deposition. So, the whole
notion of long-distance
transport of pebbles
Historical head gear on the West Rand of the Wits Basin.
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MAY 2019 MINING MIRROR [25]