Mining_Methods_UnderGround_Mining - Mining and Blasting

Pillar
between
stopes
5.0 m-high, but also the voids are filled,
providing a bench for drilling the next
slice as mining proceeds up each block.
Pillars are 5 m x 5 m at 12 m spacing.
The smaller rooms allow more selective
mining, producing a higher proportion
of processable magnesite, while the 4.4
million t of waste material dumped on
surface during chamber mining can
now be used as fill. The fill rate is up
to 300,000 t/y.
In 1971, a new rail haulage was installed,
equipped with locomotives and
20 t-capacity bottom-dump wagons.
The rail system still handles ore from
the core area of the mine, but it is more
cost effective to use truck haulage from
more peripheral parts.
Overhand stoping
Open stope
Overhand stoping room and pillar system at SMZ.
Chamber and pillar mining has created
a huge void within the mine, now totalling
13 million cu m, and undercut sections
of the hanging wall have collapsed
in places.
Studies resulted in an overhand stoping
method being introduced in some
of the mining blocks above the 323 m
level from 1990 onwards, and this now
accounts for 65% of production.
By 1998, SMZ was looking to increase
production and productivity in the overhand
stoping blocks. In consultation with
Atlas Copco, the mine trialled a Rocket
Boomer 282 equipped with a COP 1432
Pillar with loading crosscut
and transport drifts
rock drill. This rig achieved the expected
performance improvement, and was
bought by SMZ, together with a Rocket
Boomer 281 and a Simba H357, for precise
and rapid pillar recovery. The latter
unit was equipped with a COP 1838 rock
drill. Switching from pneumatic to hydraulic
drilling using the two Rocket
Boomers increased overhand stoping
magnesite output by a factor of four.
In the overhand stoped sections muck
is loaded by a fleet of three LHDs and
two wheel loaders. The LHDs typically
JelSˇ aVa, SlOVakia
tram to the ore passes that supply the
rail haulage system, while the wheel
loaders dump into trucks that may go
either to the ore passes or directly to the
primary crusher.
new level development
In 2000-2001 SMZ started to develop a
new mining level at 220 m asl. Whereas
extraction had thus far all been above
the local erosion base level, providing
natural drainage at 287 m asl, this new
level is below the water table. The amount
of water to be pumped out is equal
to the amount of ore to be extracted.
For initially driving the access ramp,
and later development, plus some production
drilling, Atlas Copco offered
SMZ a new Rocket Boomer M2 C twinboom
rig, and helped train six Simba
operators to use it.
Work on the ramp and some lateral
development started in 2001 and was
scheduled to take 3-4 years. The Rocket
Boomer M2 C normally works either
one or two of the mine’s three eighthour
shifts on the ramp, but also works
on production. The new level will be
worked in 10 m-high slices, improving
geotechnical conditions and saving on
primary development costs. However,
although many blocks of high quality
magnesite are directly accessible using
overhand stoping from the new level,
underground mining methods 71
Front
pillar
boundary
pillar
Rocket Boomer 281 drilling a crosscut entry.