Mining_Methods_UnderGround_Mining - Mining and Blasting

geOlOgy FOr Mining
geology for underground mining
importance of
geology
A thorough understanding of the
geology of a mineral deposit is
fundamental to its successful
exploitation, and this is especially
important for underground working.
As such, geology is a vital
factor in the correct selection of
mining method and equipment.
Once a mining method is chosen,
a major variance in the geology
may make it difficult to change
the approach to mining, compared
to more flexible opencast
work. This chapter reviews some
of the important basic aspects of
geology that may affect decisions
about mining method. Atlas
Copco offers a full range of drilling
products for site investigation,
and for mine development
and production. 1. Recent alluvium, lake and
sea-bed deposits e.g.
mud, sands, calcite.
2. Orebodies, e.g. containing
The earth’s crust
The earth’s crust consists of a variety
of rocks, formed under different circumstances,
and with a wide variety of
properties. Rocks usually consist of one
or more minerals, ranging from single
chemical elements to complex compounds.
There are known to be more
than 3,000 different minerals.
Of the 155 known elements, some of
which do not occur naturally, oxygen
is by far the most common, making
up about 50% of the earth’s crust by
weight. Silicon forms about 25%, and
the other common elements such as aluminium,
iron, calcium, sodium, potassium,
magnesium and titanium build up
the total to 99% of the earth’s crust.
Silicon, aluminium and oxygen occur
in the commonest minerals such as
quartz, feldspar and mica, which form
part of a large group known as silicates,
being compounds of silicic acid
and other elements. Amphiboles and py-
roxenes contain aluminium, potassium
and iron. Some of the earth’s commonest
rocks, granite and gneiss, are composed
of silicates.
galena, sphalerite,
chalcopyrite and pyrite.
3. Weathered shale, perhaps
forming bauxite.
4. Weathered sandstone, perhaps
having high quartz content.
Oxygen also occurs commonly in
combination with metallic elements,
which are often important sources for
mining purposes. These compounds
can form part of oxidic ores, such as
the iron ores magnetite and hematite.
Sulphur also readily combines with
metallic elements to form sulphide ores,
including galena, sphalerite, molybdenite
and arsenopyrite.
Other large mineral groups important
in mining include halogenides such
as fluorite and halite, carbonates such
as calcite, dolomite and malachite, sulphates
such as barite, tungstates such
as scheelite, and phosphates such as
apatite.
Rarely, some elements can occur na-
turally without combination. The important
ones are the metals gold, silver
and copper, plus carbon as diamonds
and graphite.
5. Weathered orebodies producing
azurite, malachite, cuprite, etc.
6. River valley deposits may include
gold, platinum, diamonds,
cassiterite or magnetite, as
well as clays and sands.
7. Volcanic rocks – fine-grained
minerals including feldspar,
quartz, olivine, hornblende,
magnetite and mica.
Minerals
8. Metamorphic sandstone
– high proportion of quartz.
9. Metamorphic limestone as
marble, etc – calcite and dolomite.
10. Metamorphic shales as
slates, schists, etc. – with
garnet, mica, feldspar.
11. Contact zones between
igneous and ‘country’ rocks –
garnet, hornblende, sulphides.
In some circumstances, the properties
of individual minerals can be impor-
tant to the means of mining, and will
certainly be important for the means
of extraction of the materials to be exploited.
More often, however, minerals
will be mixed with others to form the
various types of rocks, and the pro-
perties will be combined to form both
homogenous and heterogeneous struc-
tures. Feldspar accounts for almost
50% of the mineral composition of
the earth’s crust. Next come the pyrox-
ene and amphibole minerals, closely
followed by quartz and mica. These
minerals all make up about 90% of the
composition of the earth’s crust.
Minerals have a wide variety of properties
that can be important in their
usefulness to man, and to the best way
underground mining methods 7