The Anatomy of a Mine - Mining and the Environment: From Ore to Metal - page 204

Waste rock comprises all material removed from the mine other than topsoil, subsoil,
and ore. The extent of waste rock removal depends on pit geometry, which is determined
by the geometry and grade of the ore deposit, the equipment to be used and the planned
production rate of the mine. Government regulations may stipulate maximum overall
slope or batter angles which, in turn will effect the quantity of waste produced. It is the
one of the i rst tasks in surface mine design to estimate the i nal pit boundary. The pit
limit is typically established by the maximum allowable stripping ratio, a simple break-
even ratio based solely on economics. It is dei ned as the ratio of waste rock to ore at the
ultimate boundary of the pit, where the proi t margin becomes zero. In other words, the
stripping ratio indicates the point where the costs of removing and disposing of the waste
rock increase mining costs to the point where costs exceed revenue. Deposits generally
decline in grade outwards, and cutoff and pit limits may vary with economic parameters.
This means that the i nal pit size may differ from the initial estimate, depending on the
information which subsequently becomes available on the actual ore grade distribution.
The allowable stripping ratio has also a direct environmental signii cance. Since it
locates the ultimate pit boundary, it determines the amount of waste rock that needs to be
removed during mining.

The pit limit is typically
established by the maximum
allowable stripping ratio, a simple
break-even ratio based solely on
economics.

Ore extraction

Ore Drilling and Blasting
Ore breakage historically has been a drill and blast cycle. Continuous breaking is restricted
to soft rock and coal, using mechanical rotating cutters or chain-saw type devices. In-pit
drilling and sampling is commonly required to accurately dei ne the limits of the ore and
to delineate ores of different grades which may require blending to maintain a reason-
ably uniform feed to the mill, or to distinguish different ores for separate stockpiling and
treatment. This is known as 'grade control' and is the responsibility of the mine geologists.
Low grade ores may also be directed to leach dumps or pads instead of to the mill.
Environmental impacts due to drilling and blasting include dust emissions, noise, and
vibration. Visible dust plumes from blasting are classed more as an aesthetic impact or a
source of neighbourhood annoyance, rather than a health risk. For most mining opera-
tions, however, the major sources of dust emission are the haul roads rather than the more
transient dust clouds caused by blasting. Peak noise is used to assess overpressure from
blasting. Planners limit blast noise by using good stemming in drill holes, and by limiting
the Maximum Instantaneous Charge detonated simultaneously, through the incorpora-
tion of delays. Noise and vibration due to blasting are among the most noticeable effects of
mining and hence i gure prominently among complaints from neighbouring communities.

For most mining operations the
major sources of dust emission
are the haul roads rather than
the more transient dust clouds
caused by blasting.

Ore Loading and Transporting
Rock and ore materials in mining are transported by haulage or hoisting (primary vertical
movement). In open pit mining, truck teams with shovels are used/operate in most applications
( Figure 4.16 ) . In open cast mining with few benches, belt conveyors are preferred for haulage
in spite of the high investment costs for their continuous high output and low operating costs.
The main environmental impacts associated with ore loading and transportation are dust and
noise. At least half of the transport-related dust emissions are eliminated by careful watering
of the haul roads. Water sprays on ore dump stations and conveyor belt transfer points, further
reduce dust emissions. The use of covered conveyor belts practically eliminates dust emission
during haulage. Interestingly, the main source of transport noise perceived as a nuisance is the
warning noise of trucks when backing up. Night time noise is of particular concern.

In open pit mining, truck teams
with shovels operate in most
applications.