Mining_Methods_UnderGround_Mining - Mining and Blasting

Mining in flat orebodies
nearly horizontal
extraction
Variations on room-and-pillar and
longwall mining techniques have
always been attractive propositions
for mechanization, because
of the near horizontality of such
systems. Until recently, trackless
equipment was limited to a minimum
working headroom of 2 m
or more. However, major developments
in Polish copper mines
and in gold and platinum mines
in South Africa have spawned a
new generation of thin-seam and
narrow mining equipment from
Atlas Copco that can work in substantially
less space than previously
thought possible. The Rocket
Boomer S1 L, for instance, has a
tramming height of just 1.3 m, yet
can cover a face area of up to 29
sq m. Likewise, the Scooptram
ST 600LP loader equipped with
video cameras to assist the driver
has a height of only 1.56 m, but still
carries a 6 t payload. Availability
of such machines is already revolutionizing
the design approach
to mining flat orebodies.
room and pillar
Room and pillar is designed for mining
of flat, bedded deposits of limited thick-
ness. Examples are sedimentary deposits,
like copper shale, limestone or
sandstone containing lead, coal seams,
salt and potash layers, limestone and
dolomite.
The method recovers the mineraliza-
tion in open stopes, leaving pillars of
ore to support the roof. To recover the
maximum amount of ore, miners aim to
leave smallest possible pillars behind,
because these are difficult and expen-
sive to recover. The roof must remain
intact, and rockbolts are used extensively
as rock reinforcement. Rooms
and pillars are normally arranged in
regular patterns, and can be designed
with circular pillars, square pillars, or
elongated walls separating the rooms.
Classic room and pillar applies to
flat, bedded deposits with moderate to
Vertical benching
Benching of thicker parts
Classic room and pillar layout.
large thickness, also to inclined deposits
with larger thickness. Mining the
orebody creates large openings, where
trackless machines can travel on the
flat floor. Orebodies with large vertical
height are mined in horizontal slices,
starting at the top and benching down
in steps.
Post room and pillar applies to inclined
orebodies, of dip angle from 20
to 55 degrees, with large vertical height,
where mined out space is backfilled.
The fill keeps the rock mass stable,
and serves as the work platform while
mining the next ore slice.
Step room and pillar is an adaptation
of trackless mining to orebodies with
too steep a dip for rubber-tyred vehicles
to operate in a regular room and
pillar layout. Haulage drifts and stopes
are therefore angled diagonally across
the dip, to create work areas with level
floors off which trackless equipment
can work. Mining advances downward,
along the step room angle.
Classic room and pillar
Very little development work is required
to prepare flat-bedded deposits for room
and pillar mining, because access for
ore transport and communication is
through the production rooms.
FlaT Mining
Ore production in flat room and pillar
uses the same drill/blast techniques
as in normal drifting. Where geological
conditions are favourable, large-capacity
drilling rigs and loaders can be used.
High orebodies are mined in slices,
starting at the top, rockbolting the roof
from each bench. Standard crawler rigs
are used for drilling vertical holes and
conventional bench blasting. Horizontal
drilling and flat benching is a more prac-
tical alternative, using the same drilling
equipment.
The blasted ore is loaded using
diesel or cable-electric LHD machines,
and, where height permits, dump trucks
may be used between stope and dump.
In thin orebodies, loading points may
be necessary for transferring ore from
loader to hauler. As all activities are car-
ried out on one or very few levels covering
a large area, there are many faces available
at any time, so high equipment utili-
zation is possible.
Post pillar
© Atlas Copco Rock Drills AB, 2000
Post pillar mining is a crossbreed of room
and pillar and cut and fill mining. Post
pillar mining recovers the mineralization
in horizontal slices, starting from a
bottom slice, advancing upwards. Pillars
are left inside the stope to support the
underground mining methods 39
Pillar
Pillar