Why Quarrying?

Why Quarrying?
In South Africa, ASPASA has found that the understanding of “Quarrying” is often not understood and
the difference between a mine and quarry is not understood. This section has been developed to
provide the public with an overview of quarrying and its importance to South Africa’s economy and
overall growth.
AN INTRODUCTION TO QUARRYING
Stone is the most widely used construction material in the world. It s use goes back to the dawn of
civilisation. When some 4,000 years ago men cut stone to build the known structures of the Cheops
Pyramid in ancient Egypt and the historical site at Stonehenge in Great Brittan, quarrying activities
were already well established in many areas of the world. The Great Wall of China, constructed over
2,000 years ago, consumed staggering quantities of stone that was provided by the quarry industry in
that region.
The demand for quarried aggregates is enormous. Quarries underpin the ongoing development and
maintenance of our country. Stone is an essential component used in the construction of homes,
factories, schools, hospitals and shopping centres, soccer stadiums, etc. Road, railways, airports
and port construction consumes large volumes of aggregates in every form, as does the ongoing
forestry and rural development. Construction initiatives are supported by the use of stone to protect
landforms.
The quarry industry produces many millions of tonnes annually for use by the home building industry.
Depending on design and site conditions, over 4,000 tonnes of aggregates are used in the
construction of just one kilometre of standard highway pavement, while the building of a new six lane
motorway can consume in excess of 20,000 tonnes for the same distance.
Thus the quarrying and aggregate production industry plays a vital role in the nation’s economy, not
only by providing essential materials but also by providing employment opportunities which are in
many cases in rural areas.
MINERAL WEALTH IN SOUTH AFRICA
The earth abounds in the deposits of different minerals. Included in our wealth is stone and rock for
aggregates, limestone deposits which are used in the manufacture of fertilisers, cement, for road
surface rehabilitation, and a range of clays for bricks, ceramics and pottery products.
1The aggregates are obtained from the extraction and processing of rock or stone from two main
sources. These are Quarries and Riverbeds.
Revision No. 1
Revision Date: January 2014
www.aspasa.co.za
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Quarrying
Quarries
The first source is a quarry where rock is obtained by blasting a quarry face, then crushing and
screening material to produce a wide range of aggregates in various sizes and to specified quality
limits. There are three basic types of rock used to produce most quarried rock aggregates.
1. Igneous: rock which formed as a result of volcanic activity and then solidified from molten lava
flow. Examples are basalt and andesite rock.
2. Sediment: rock which formed in the distant past by the settlement fine sand and grit under
pressure on a seabed. Greywacke and limestone deposits are most common.
3. Metamorphic: rock e.g. quartz is formed by the action of heat and /or pressure on existing
rock formations.
Riverbeds
Gravels and sand, the second major source of aggregates, are found by the past natural erosion of
existing rock and then transported by ice or water to be deposited in old or existing riverbeds or into
the sea. These deposits normally consist of rounded, separate particles and are more easily extracted
than the quarried material. The smaller sized stone, (minus 25mm) is usually sold in an uncrushed,
washed state for use in the concrete production. The larger sizes and boulders can be crushed and
processed into nominated product specifications.
Soil, clay or other soft or weathered materials which normally overlay quarry resources and land
based gravel deposits is termed overburden. If the depth of overburden is too great then it may be
uneconomical to attempt the extraction of rock or gravel at a specific site,
EXTRACTION & PROCESSING
In the past hard rock quarrying was undertaken by the use of manual labour. The tasks were hard,
backbreaking and often dangerous for the labour force.
Today the two main sources of aggregates are extracted in different ways. Quarried rock is now
normally broken out from the main faces by means of controlled blasting. Each blast is well planned to
provide a measured quantity of loose rock whilst minimising ground vibration and noise within the
immediate surrounding area. Blasting usually occurs at preset times and where necessary a system
of prior warning for neighbours is put in place.
Gravel and sand excavated from dry pits or river beds generally do not require blasting to loosen the
resource. Hydraulic excavators and Front End Loaders are normally use for this task. A wide variety
of mechanical loaders are employed within the industry to load the blasted rock or excavated gravels
on to waiting dump trucks, in preparation for haulage to the crushing, screening and washing plants.
At the processing plant an array of jaw, gyratory and impact crushers followed by various washing
systems and screening units transform the raw material into a range of quarry products. These
products vary from very tightly specified crushed or uncrushed screened and graded rock and stone
for use in highway construction, to a selection of lower quality material, which is used for general nonspecified roading works. Often the higher quality products are combined with other materials such as
cement to manufacture concrete or bitumen to produce asphalt pavement surfacing