Mining_Methods_UnderGround_Mining - Mining and Blasting

Atlas Copco underground core drilling rig Diamec U4.
specialities, the main one being to de-
tect the presence of metals in the topsoil
cover. By taking a large number of
samples over an extended area and
analyzing the minute contents of each
metal, regions of interest are identified.
The area is then selected for more
detailed studies.
exploratory drilling
For a driller, all other exploration me-
thods are like beating about the bush.
Drilling penetrates deep into the ground,
and brings up samples of whatever it
finds on its way. If there is any mineralization
at given points far beneath the
surface, drilling can give a straightforward
answer, and can quantify its
presence at that particular point.
There are two main methods of exploratory
drilling. The most common,
core drilling, yields a solid cylinder
shaped sample of the ground at an
exact depth. Percussion drilling yields
a crushed sample, comprising cuttings
from a fairly well-determined depth
in the hole. Beyond that, the drillhole
itself can provide a complementary
amount of information, particularly by
logging using devices to detect physical
anomalies, similar to the geophysical
surveys mentioned above.
Core drilling is also used to define
the size and the exact borders of minera-
lization during the lifetime of the mine.
This is important for determining ore
grades being handled, and vital for calculating
the mineral reserves that will
keep the mine running in the future. A
strategically-placed underground core
drill may also probe for new ore bodies
in the neighbourhood.
Core drilling
In 1863, the Swiss engineer M Lescot
designed a tube with a diamond set face,
for drilling in the Mount Cenis tunnel,
where the rock was too hard for conventional
tools. The intention was to explore
rock quality ahead of the tunnel face,
and warn miners of possible rock falls.
Mineral PrOSPeCTing and exPlOraTiOn
This was the accidental birth of core
drilling, a technique now very widely
used within the mining industry. Core
drilling is carried out with special drill
rigs, using a hollow drill string with an
impregnated diamond cutting bit to re-
sist wear while drilling hard rock. The
crown-shaped diamond bit cuts a
cylindrical core of the rock, which is
caught and retained in a double tube
core-barrel.
A core-catcher is embedded in, or
just above, the diamond bit, to make
sure that the core does not fall out of the
tube. In order to retrieve the core, the
core-barrel is taken to surface, either by
pulling up the complete drill string or,
if the appropriate equipment is being
used, by pulling up only the inner tube
of the core-barrel with a special fishing
device run inside the drill string at the
end of a thin steel wire.
The core is an intact sample of the un-
derground geology, which can be examined
thoroughly by the geologist to
determine the exact nature of the rock
and any mineralization. Samples of
underground mining methods 15