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design the layout correctly from the start
and take the most important economic
modifying factors into consideration.
Detailed studies
Introducing geophysical methods
Geophysical methods are employed during
this stage and the most common methods
used are very low frequency electromagnetic
/ radio frequency electromagnetic (VLF-EM/
RF-EM) and the ground-penetrating radar
(GPR) techniques. The VLF-EM/RF-EM
method identifies major structures and the
delimitation of features such as clay-filled
fractures. GPR survey has a penetration
depth of 10 to 25m and gives a large cross
section of the subsurface fracturing and can
determine zones of significant weakness,
dykes and contacts.
A deep drilling programme is then
undertaken to describe the deposit at
depth. Diamond core drilling is preferable,
as the core can be evaluated for colour
A dimension stone quarry, like most
mining operations, starts with a desktop
study, which takes into consideration
the geological setting and any adjacent
quarries in production. The desktop study
also includes a detailed market study and a
consideration of the economic drivers for
dimension stone.
As the deposit is the one factor that cannot
be changed in a dimension stone project, it is
crucial to conduct a detailed geological study.
The cost of such a study is small compared to
other mining endeavours, but crucial to the
success of a dimension stone quarry.
Identification of the target area is
usually done by remote sensing for viable
outcrop. Once a suitable area has been
identified, the legal applications in terms
of a prospecting permit and environmental
management plan needs to be obtained.
The conversion of the prospecting right
to a mining right will generally be done
quickly as the geological investigation is
more high-level than for conventional
exploration of minerals.
The field evaluation entails establishing
the general soundness and appearance
of the stone, particularly the grain size
and colour of the stone. Grab and drilled
samples are collected to be polished
and evaluated. The features that are
described in the outcrop include: colour
variations, textural characteristics and
textural variation, structural and macro-
discontinuities, micro-discontinuities,
intrusions, inclusions, accessory minerals,
contact zones and alterations.
The initial field descriptions will also
mention boulder size as that is an indication
of the average size ranges that the outcrop
will break into. Mapping of the outcrop
is done in traverses. To be able to map
discontinuities and faults, the outcrop can be
cleaned by mechanical means, compressed
air or pressurised water jets.
The outcrop is mapped in detail on a scale
of between 1:100 and 1:250 to suit the size of
the deposit. Elements noted on the geological
maps are rock composition, colour and
structure of the stone, including fracturing.
The next step is to get a 3D grasp of the
physical features of the outcrop.
A dimension stone block yard.
QUARRY SA | MAY/JUNE 2018 _ 11
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