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