Mining_Methods_UnderGround_Mining - Mining and Blasting
Mining_Methods_UnderGround_Mining - Mining and Blasting
Mining_Methods_UnderGround_Mining - Mining and Blasting
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
%<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
Canada latin<br />
america<br />
exploration drilling will not be carried<br />
out by the same people, so reliability of<br />
information is critical. There are many<br />
reasons why geologists should choose<br />
their drilling method carefully.<br />
If there is no need for continuous information<br />
about the geological formation<br />
on the way down, there is no need<br />
for samples. It is just a matter of minimizing<br />
the drilling time. The geometry<br />
of the orebody is already known, <strong>and</strong><br />
just a reconfirmation of the boundaries<br />
is necessary. In this case, RC drilling is<br />
an efficient method to use.<br />
A first scanning of virgin territory<br />
is being done where the goal is just to<br />
obtain a preliminary indication of possible<br />
content. In this case, the geologist<br />
is not relying on any mineralized struc-<br />
ture or geometry. With an evaluation<br />
giving positive results, a programme of<br />
core drilling is the logical way to con-<br />
tinue in order to bring the project to a<br />
resource/reserve status.If the minera-<br />
lized structure is identified but the<br />
geometry <strong>and</strong> rate of content varies,<br />
RC drilling is used as an indicator for<br />
ensuring continued grade control.<br />
The geologist wants dry <strong>and</strong> repre-<br />
sentative samples in order to make opti-<br />
mal evaluations. RC drilling below the<br />
groundwater table was previously believed<br />
to undermine sample quality.<br />
Core drilling therefore remained the<br />
only viable method for these depths<br />
Today, the availability of high pressure<br />
compressors <strong>and</strong> hammer tools makes<br />
it possible for RC drilling to reduce<br />
costs even for these depths.<br />
These days, professional contractors<br />
deliver dry sampling down to depths<br />
russia<br />
China<br />
of 500 m. By sealing off the bit from<br />
the rest of the hole it can be kept dry.<br />
A correct selection of shroud vs bit tolerance<br />
maintains a pressurized zone<br />
around the bit. Boosted air pressure is<br />
needed to meet the higher water pressure<br />
on its way down the hole. In addition,<br />
a dry bit drills faster.<br />
It must be remembered that infor-<br />
mation from a core is crucial in esti-<br />
mating the period of mineralized struc-<br />
tures. The core helps the geologist to<br />
calculate the cost of extracting the<br />
mineral from the ore. Large volumes of<br />
rock have to be excavated to obtain just<br />
a few grammes of a valuable mineral.<br />
Cores also yield geotechnical data.<br />
Data about slope stability can be of the<br />
highest importance. Ground conditions<br />
are naturally also of great importance<br />
<strong>and</strong> may produce questionable samples<br />
if some of the information from<br />
fissured zones is left behind in the<br />
hole <strong>and</strong> not collected. In such circumstances,<br />
core drilling could be the only<br />
alternative.<br />
increased usage of<br />
rC drilling<br />
RC drilling is on the increase, <strong>and</strong> may<br />
well account for 55% of all metres<br />
drilled in 2008. The diagram above<br />
shows some estimated ratios between<br />
core <strong>and</strong> RC drilling in different parts<br />
of the world in 2002. In terms of metres<br />
drilled, RC accounts for 50% <strong>and</strong> core<br />
drilling for 50%. Tradition <strong>and</strong> environ-<br />
mental impact play large roles. RC rigs<br />
are heavy, <strong>and</strong> are mounted on trucks<br />
or track carriers. This fact tends to<br />
rigHT BalanCe<br />
australia Se asia uSa africa<br />
Ratios between core <strong>and</strong> RC drilling. The figures reflect total exploration expenditures from national statistics for surface <strong>and</strong> underground.<br />
favour core drilling rigs, which are much<br />
lighter <strong>and</strong> more adaptable in order<br />
to be flown into remote <strong>and</strong> sensitive<br />
environments.<br />
In areas with extremely cold climates<br />
<strong>and</strong> where permafrost is present, RC<br />
drilling may have its limitations. Antifreeze<br />
rock drill oil can help to keep<br />
the hammer <strong>and</strong> bottom of the hole free<br />
from ice. Other purely practical issues<br />
determine the choice of one or the other<br />
drilling method.<br />
An intelligent, balanced choice be-<br />
tween the two methods is the key to<br />
optimal results. The geologist plays an<br />
extremely important role in finding this<br />
balance, as do the manufacturers such<br />
as Atlas Copco Geotechnical Drilling<br />
<strong>and</strong> Exploration, who continue to provide<br />
the right tools for the job.<br />
Explorac 220RC.<br />
Jan Jönsson<br />
rC drilling<br />
Core drilling<br />
underground mining methods 19