Mining in focus
“This is actually only a fragment of the area
actually covered by the glacial deposits, as
other parts have since broken away and are
now located in Australia and India, and
possibly elsewhere.
“The notion of ice transport may sound far-
fetched, but this is exactly what happened in
North America during the last ice age, which
began about two million years ago and ended
only 10 000 years ago,” Professor McCarthy
continues.
The glacial theory could potentially be
a revolutionary paradigm shift for gold
exploration in South Africa. What it means
is that the concept of a distinct source away
from which the gold concentration gets
poorer, doesn’t apply. Glaciers can move
massive quantities of rock over huge
distances; in other words, they can
spread gold over vast areas, so
vast that the original sources
become indistinct and impossible to trace.
In fact, repeated cycles of sediment transport
by ice, deposition of gold-bearing gravel,
re-transport of the gravel during renewed
ice advance, re-concentration of gold during
ice melting, and so forth, lasting hundreds of
thousands to millions of years, would create a
multiplicity of secondary gold sources, and
the original source would
be lost.
We see a modern
example in North America.
Most of the alluvial gold
in the northern states of
the US and Alaska came
from multiple sources
in Canada, was brought
and gold by ice began to make sense. The
melting of the ice generated lots of water,
which concentrated the gold into the gravel
(conglomerate) beds we see today,” Professor
McCarthy explains.
He continues: “The flowing water washed
away the less dense and smaller particles and
concentrated the pebbles and dense gold
grains. The critical step was the initial ice
transport. Advance of ice sheets across the
developing Witwatersrand Basin dispersed
and deposited glacial debris in the form of
puddingstone (tillite). This material was
washed and reworked by melt water during
glacial retreat. Repeated cycles of ice advance
and retreat, lasting perhaps millions of
years, spread gold-bearing gravel
over the vast Witwatersrand
Basin, which at that time
extended at least from
Polokwane in the
north to Colesberg
in the south-west
and to Swaziland in
the south-east.
Many ounces of gold are still locked up in the old mining dumps of Johannesburg.
[26] MINING MIRROR MAY 2019
www.miningmirror.co.za