BUSINESS
Dimension stone cuts can be done in one
of two ways, the first is to have a standard
and the second is to optimise the size of
blocks recovered. The advantage of the
standard is that blocks of uniform size will
be produced, but significantly more waste
material is produced with a lower block
recovery / yield. The optimised grid cut will
yield larger blocks and minimise waste but
require secondary sizing of the blocks if
demanded by the market or due to slabbing
equipment limitations.
The dimensions of a bench are
determined by physical factors and
equipment limitations. The length is
restricted by the limits of accurate drilling
for the intersecting holes of the diamond
wire cuts. The width of the bench is
determined by the limits of accurate
drilling and blasting, and the height of the
bench is determined by the block handling
equipment.
The choice of mining method in a
dimension stone quarry is completely
dependent on the geology of the deposit.
Boulder formations will largely be quarried
by means of splitting methods, most
commonly using specialised blasting
techniques. Solid formations may require
a combination of different methodologies.
Marbles, slates, sandstones and quartzites
are quarried by non-explosive splitting and
cutting techniques.
Granite and dolerites on the other
hand require blasting techniques. The
main consideration in the type of blasting
technique is the prominence of cleavage/
weakness planes in the rock along with
minimising the amount of blast induced
cracking that will reduce the quality of the
saleable blocks.
Conventional mining of solid formations
of marble and granite make use of diamond
wire sawing to loosen large benches, which
are then split into successively smaller
blocks until these are of a size that can be
handled by the loader or crane. The blocks
are removed from the face and trimmed
if necessary to square it and remove any
remaining defects.
By optimising the mining layout and
extractions methods, you can better manage
the challenges imposed by the dimension
stone market, such as a ‘fashionable’
product versus the commodity in the
ground, the customer derived demand,
price elasticity, industry structure and
competing products. ■
CREDIT
Bowline Professional Services:
www.bowlineps.co.za.
“The choice of mining
method in a dimension
stone quarry is
completely dependent
on the geology of the
deposit.”
QUARRY SA | MAY/JUNE 2018 _ 13