WINNING
I
n planning the layout of an opencast
mining operation or a quarry, the main
factors that will determine the layout
and the potential for profitability are the
geological characteristics of the deposit and
the economic considerations to first bring
the operatio n into production, including
the costs associated with running it.
Geological factors
Opencast and quarry operations target
deposits that outcrop on surface or near
surface. Opencast mining operations
usually target bulk commodities such as
iron, manganese, coal, and similar type
deposits. The product is sold unprocessed
as lumpy ore, or with minor beneficiation,
such as washing or pelletising. Quarry
operations target industrial materials
such as sand, gravel, dimension stone,
and related materials that are mostly sold
after crushing and screening or sizing.
The geological and topographical features
determine the extent of mining.
Mining shallow deposits will start
off with a desktop study to find suitable
deposits or to infer the extent of adjacent
mines. This will usually also entail a
remote sensing component, such as
orthophotos or satellite spectral images.
Once the legal requirements such as
prospecting and mining right applications,
environmental impact assessments,
environmental management plans, and
public consultation have been completed,
sampling of the deposit takes place. Grab
samples are collected from the surface,
which is used to create geochemical
surface maps for opencast mines or
material quality domain maps for quarries.
This would generally be done in parallel
with geophysical studies to delineate the
extent of the mineralisation and to detect
subsurface structures that are not visible
during surface geological mapping.
The next step is to conduct drilling.
A combination of core and chip drilling
is done to determine the lithology and
mineralisation at depth. The surface grab
samples and drill core or chip samples are
dispatched for assaying to determine the
grade. The sample material is also used in
metallurgical tests to determine the best
recovery methods, which will influence the
QUARRY SA | ULY/AUGUST 2018 _ 13