Mining Methods Vary Widely - Mining and the Environment: From Ore to Metal - page 229

5.2 MINING METHODS

The most common mining methods are surface, underground and solution mining subdivided
into various classes and subclasses as illustrated in Figure 5.4 . Since the range of environmental
concerns associated with mining is discussed in detail in Chapter Thirteen, the following sec-
tions address only those environmental impacts associated with a particular mining method.

Surface Mining

Surface mining has been discussed in detail in Chapter Four and we will revisit the two
main types of surface mining, open pit and strip mining, only briel y.
Iron ore, stone, gravel and many other minerals and ores are extracted by open pit
mining, in which a hole is excavated into the Earth's surface. Overburden, if present, is
stripped and placed outside the pit area to uncover the mineral deposit. The pit excavation
usually produces additional large volumes of waste rock that need to be removed to pro-
vide access to the ore and to create stable slopes. The ore is usually separated from waste
materials (either overburden or adjacent host rock) within the pit during excavation. Rock
fragmentation (that is drilling and blasting) and laboratory testing of samples recovered
during the drilling programme prior to blasting allows the mining engineer to classify
waste rock and ore type for selective placement or, respectively, treatment. It is at this stage
that the detailed characteristics of the ore body become apparent.
Strip or open cast mining, used for near-surface laterally extensive deposits such as coal
seams, stratii ed ores or lateritic deposits such as bauxite or nickel laterites, resembles open
pit mining but differs in one unique aspect: overburden is hind-cast or transported a short
distance into adjacent mined-out panels. Mine rehabilitation can be carried out progres-
sively at the same rate as mining.
Most mineral products and coal are extracted by surface mining. Surface mines are
large-scale operations moving very large volumes of materials. By contrast, underground
mining produces much lower volumes. Climate, topography, and existing land cover and
use are more critical to surface than underground mining operations. In surface mining,
most physical and chemical environmental impacts are directly related to extracting and
relocating large amounts of rock materials.

Most mineral products and coal
are extracted by surface mining.

Underground mining

Underground mining is more complex than surface mining. While surface mining can
be characterized as a mass production of ore and associated mine waste at minimal cost,
underground mining aims to target the main ore body with minimal waste rock removal.
Overall mining costs may be similar; however, the unit excavation cost in underground
mining is much higher.
Access to underground mines may be by means of vertical shafts, horizontal drives also
known as adits, or by declines which are inclined tunnels. In a shaft mine, one or more ver-
tical shafts connect the deposit to the surface. The ore is fragmented underground and then
hoisted in buckets or skips, up through the shaft to the surface. Where adits or declines are
used the broken ore can be hauled out of the mine in rail trucks or conventional trucks.
If further crushing takes place underground, conveyors may be used to transport the ore
along adits or declines. Each underground mine is different in the way ore is accessed and
fragmented, but underground mines differ little in their environmental impacts.

Underground mining aims to
target the main ore body with
minimal waste rock removal.