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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geOlOgy FOr <strong>Mining</strong><br />
to mine or tunnel through them, or both.<br />
Some of these important characteristics,<br />
which are also important for correct<br />
mineral identification in the field<br />
before chemical analysis, are hardness,<br />
density, colour, streak, lustre, fracture,<br />
cleavage <strong>and</strong> crystalline form.<br />
The particle size, <strong>and</strong> the extent to<br />
which the mineral is hydrated or other-<br />
wise mixed with water, can be very im-<br />
portant to the behaviour of the rock<br />
structure when excavated. Mineral hard-<br />
ness is commonly graded according to<br />
the Moh 10-point scale<br />
The density of light-coloured minerals<br />
is usually below 3. Exceptions are<br />
barite or heavy spar (barium sulphate<br />
– BaSO 4 – density 4.5), scheelite (calcium<br />
tungstate – CaWO 4 – density 6.0)<br />
<strong>and</strong> cerussite (lead carbonate – PbCO 4<br />
– density 6.5). Dark coloured minerals<br />
with some iron <strong>and</strong> silicate have<br />
densities between 3 <strong>and</strong> 4. Metallic ore<br />
minerals have densities over 4 Gold has<br />
a very high density of 19.3. Minerals<br />
with tungsten, osmium <strong>and</strong> iridium are<br />
normally even denser.<br />
Streak is the colour of the mineral<br />
powder produced when a mineral is<br />
scratched or rubbed against unglazed<br />
white porcelain, <strong>and</strong> may be different<br />
from the colour of the mineral mass.<br />
Fracture is the surface characteristic<br />
produced by breaking of a piece of the<br />
mineral, but not following a crystallographically<br />
defined plane. Fracture<br />
is usually uneven in one direction or<br />
another.<br />
Cleavage denotes the properties of<br />
a crystal whereby it allows itself to be<br />
split along flat surfaces parallel with<br />
certain formed, or otherwise crystallographically<br />
defined, surfaces. Both<br />
fracture <strong>and</strong> cleavage can be important<br />
to the structure of rocks containing sub-<br />
stantial amounts of the minerals concerned.<br />
Proper ties<br />
Rocks, normally comprising a mixture<br />
of minerals, not only combine the properties<br />
of these minerals, but also exhibit<br />
properties resulting from the way in<br />
which the rocks have been formed, or<br />
perhaps subsequently altered by heat,<br />
pressure <strong>and</strong> other forces in the earth’s<br />
Moh’s hardness Typical mineral Identification of hardness<br />
scale<br />
1 Talc Easily scratched with a fingernail<br />
2 Gypsum Barely scratched with a fingernail<br />
3 Calcite Very easily scratched with a knife<br />
4 Fluorite Easily scratched with a knife<br />
5 Apatite Can be scratched with a knife<br />
6 Orthoclase Difficult to scratch with a knife, but<br />
can be scratched with quartz<br />
7 Quartz Scratches glass <strong>and</strong> can be<br />
scratched with a hardened steel file<br />
8 Topaz Scratches glass <strong>and</strong> can be<br />
scratched with emery board/paper<br />
(carbide)<br />
9 Corundum Scratches glass. Can be scratched<br />
with a diamond<br />
10 Diamond Scratches glass <strong>and</strong> can only be<br />
marked by itself<br />
crust. It is comparatively rare to find<br />
rocks forming a homogeneous mass,<br />
<strong>and</strong> they can exhibit hard-to-predict<br />
discontinuities such as faults, perhaps<br />
filled with crushed material, <strong>and</strong> major<br />
jointing <strong>and</strong> bedding unconformities.<br />
These discontinuities can be important<br />
in mining, not only for the structural<br />
security of the mine <strong>and</strong> gaining access<br />
to mineral deposits, but also as paths<br />
for fluids in the earth’s crust which<br />
Samples of common rock types<br />
Amphibolite.<br />
Dolomitic limestone.<br />
cause mineral concentrations. In order<br />
for mining to be economic, the required<br />
minerals have to be present in sufficient<br />
concentration to be worth extracting,<br />
<strong>and</strong> within rock structures that can be<br />
excavated safely <strong>and</strong> economically. As<br />
regards mine development <strong>and</strong> production<br />
employing drilling, there must be a<br />
correct appraisal of the rock concerned.<br />
This will affect forecast drill penetration<br />
rate, hole quality, <strong>and</strong> drill steel<br />
costs, as examples.<br />
One must distinguish between microscopic<br />
<strong>and</strong> macroscopic properties, to<br />
determine overall rock characteristics.<br />
As a rock is composed of grains of various<br />
minerals, the microscopic properties<br />
include mineral composition, grain<br />
size, the form <strong>and</strong> distribution of the<br />
grain, <strong>and</strong> whether the grains are loose<br />
or cemented together. Collectively, these<br />
factors develop important properties of<br />
the rock, such as hardness, abrasiveness,<br />
compressive strength <strong>and</strong> density. In<br />
turn, these rock properties determine the<br />
penetration rate that can be achieved,<br />
<strong>and</strong> how heavy the tool wear will be.<br />
In some circumstances, certain mineral<br />
characteristics will be particularly<br />
important to the means of excavation.<br />
8 underground mining methods