Mining_Methods_UnderGround_Mining - Mining and Blasting

Increasing level
of geological
knowledge and
confidence
Mineral PrOSPeCTing and exPlOraTiOn
special interest are sent to a laboratory
for analysis to reveal any metal contents.
Cores from exploration drilling
are stored in special boxes and kept in
archives for a long period of time. Boxes
are marked to identify from which hole,
and at what depth, the sample was taken.
The information gathered by core
drilling is important, and represents substantial
capital investment.
Traditionally, core drilling was a very
arduous job, and developing new techniques
and more operator-friendly equip-
ment was very slow, and the cost per
drilled metre was often prohibitive. Atlas
Copco Geotechnical Drilling and Explo-
ration pioneered several techniques to
reduce manual work, increase efficiency
and cut the cost per drilled metre.
Over the years, the company developed
thin walled core barrels, diamond impreg-
nated bits, aluminium drill rods, fast
rotating hydraulic rigs, mechanical rod
handling, and, more recently, partly or
totally computer-controlled rigs. Core
drilling has always been the most power-
ful tool in mineral exploration. Now that
it has become much cheaper, faster and
easier, it is being used more widely.
reverse circulation
drilling
Exploration Results
To obtain information from large ore-
bodies where minerals are not concentrated
in narrow veins, reverse circulation
Mineral Resources Ore Reserves
Inferred
Indicated
Probable
Measured Proved
Consideration of mining, metallurgical, economic, marketing,
legal, environmental, social and governmental factors
(the ”modifying factors”)
The 2004 Australasian code for reporting exploration results, mineral resources and ore reserves.
drilling is used. Reverse circulation dril-
ling is a fast, but inaccurate, exploration
method, which uses near-standard
percussion drilling equipment. The
flushing media is introduced at the
hole collar in the annular space of a
double-tubed drill string, and pushed
down to the bottom of the hole to flush
the cuttings up through the inner tube.
The drill cuttings discharged on surface
are sampled to identify variations
in the mineralization of the rock mass.
Reverse circulation drilling uses much
heavier equipment than core drilling,
and has thus a limited scope in depth.
From prospecting to
mining
Every orebody has its own story, but
there is often a sequence of findings.
After a certain area catches the interest
of the geologists, because of ancient
mine works, mineral outcrops or geological
similarities, a decision is taken
to prospect the area. If prospecting con-
firms the initial interest, some geophysical
work might be carried out. If interest
still persists, the next step would be
to core drill a few holes to find out if
there is any mineralization.
To quantify the mineralization, and
to define the shape and size of the ore
body, then entails large investment to
drill exploratory holes in the required
patterns.
At every step of the procedure, the
geologists examine the information at
hand, to recommend continuing the exploration
effort. The objective is to be
fairly certain that the orebody is eco-
nomically viable by providing a detailed
knowledge of the geology for a clear
financial picture. Ore is an economic
concept, defined as a concentration of
minerals, which can be economically
exploited and turned into a saleable
product.
Before a mineral prospect can be
labelled as an orebody, full knowledge
is required about the mineralization,
proposed mining technology and processing.
At this stage a comprehensive
feasibility studied is undertaken covering
capital requirements, returns on
investment, payback period and other
essentials, in order for the board of di-
rectors of the company to make the
final decision on developing the prospect
into a mine.
When probabilities come close to
certainties, a decision might be taken to
proceed with underground exploration.
This is an expensive and time-consuming
operation, involving sinking a shaft
or an incline, and pilot mining drifts and
galleries. Further drilling from underground
positions and other studies will
further establish the viability of the
orebody.
After the mineralization has been
defined in terms of quantity and quality,
the design of mine infrastructure starts.
The pictures on page 14 show recent
plans at the Suurikuusikko gold mine
project in Finland where the optimum
mining methods combine both open pit
and un-derground mining. Production
can start in the open pit while preparing
for the underground operation.
With an increasing level of geological
information the mineral resources
get better confirmed. The feasibility
study will take into consideration all
economical aspects, as well as the effects
of the selected mining method.
Depending on the mining method, there
could be essential differences between
mineral resources and ore reserves, both
in terms of quantity and grade.
Hans Fernberg
16 underground mining methods