Gemstone Extraction Techniques
Reference: Yahoo Babel Fish
Extraction of Rough Gemstones from the Ores:
The process of extracting the gemstones from the ores varies from
place to place and is dependent on the nature and quality of the
gemstone. In general those from alluvial deposits are assorted by
washing with sieves.

Slurry containing the gemstone rough along with mud and
other materials is washed with water on a sieve. A vibratory
motion is applied to the sieve so as to separate the slurry
quicker. The gem rough is then hand picked from the sieves.
Depending on the size of the rough, different sieve sizes are
employed. This method is commonly employed for most
gemstones.
Extraction of Rough Diamonds from the Ores:
In the case of Diamond extraction from the mother rock, the process
is more complicated. The entire process however utilizes the
properties of diamonds to separate them. Following are the basic
processes by which diamonds are recovered from the ore.
1. Crushing: Done to reduce the size of the rocks in the ore.
2. Heavy Media Separators: Make use of the property of
specific gravity wherein a heavy stone will sink in a liquid of
lower specific gravity. Either one or a series of Heavy Media
Separators are used to separate the diamonds. A centrifugal
force is applied to the liquid inside, for faster separation.
3. Grease Table or Belt: Uses the property that diamonds stick
to grease. The ore is poured over this table and washed with
water. A vibratory motion is given to the table. The diamonds
with a few other minerals stick to the table while the rest is
washed off. Heat is used to separate the diamonds from the
grease.
4. X - Ray Separators: Uses the principle that diamonds
fluoresce to X - rays. The ore is dropped in a fine stream
through a channel and an X- ray beam is directed at it. As a
diamond fluoresces, a detector activates an airjet and the
diamond is directed into another channel.
5. Magnetic Separators: In areas where there are magnetic
minerals present in the ore, a magnetic belt is used for
separation.
The material which is discarded, also known as tailings, after going
through the processes in a treatment plant is sometimes re-checked
and is considered in the evaluation of the efficiency of the plant. The
diamonds which have been separated are now washed in acid and
cleaned, ready for assortment. Diamonds which are coated will
probably not react well to the above processes. Under the
circumstances, the quality of the rough should be ascertained before
the specific processes are employed.
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Mining:
The methods used in the mining of gem materials are many, from
native mining to highly technical methods.

Gemstone Mining
1. Open Cast Mining
1. Pit Mining
2. Terrace Mining
2. Underground Mining
1. Tunneling
2. Block Caving
3. Chambering
3. Water Bodies
1. River Diggings
1. Dry Diggings
2. Wet Diggings
2. Sea
1. Tidal
2. Undersea or Marine Mining

Open Cast Mining:
It includes the removal of overlying minerals or rocks to reach
the gem bearing rocks. The gem - bearing rocks are then
washed by jets of water under high pressure or by traditional
methods to obtain the gem gravels. These gravels are then
washed and assorted at the treatment plants. Opencast
mining is done in many parts of the world e.g. Myanmar, Sri
Lanka, U.S.A., Brazil etc.
o Pit mining is the term used to describe a mining
method where pits are dig up to about 12 meters. Open
cast mining operations are generally initiated by pit
mining.
o Terrace mining is the term used to describe a mining
method where the gem bearing rocks are exposed by
digging horizontal terraces in step-like, generally circular
formations. Blasting or digging is done and the debris is
then washed to obtain the gem gravels. Emerald mining
in Columbia (Chivor Mine) is the best example of terrace
mining.

Underground Mining:
This includes mining from alluvial and pipe deposits. In the
case of alluvial deposits where pit mining is done, deeper pits
of over 10 metres are considered by some as a form of
underground mining.
o Tunneling technique is employed when there is a gem bearing rock either as an outcrop or as a seam running
close to the surface. A tunnel is made from the surface
to the gem - bearing rock and mining is done by blasting
or by using pick axes to remove individual gem rough.
This type of mining is seen at a few emerald mines in
Columbia.
o In Block caving, a series of parallel tunnels called
scraper drifts are driven from the main shaft into the
pipe, about 400 to 600 feet below the top of the mother
rock. Starting at the top level, whole blocks of blue
ground are mined out by blasting of the roof of the
tunnels through conical draw points into the scraper
drift. This is then transported to the main shaft and then
to the surface.
o In Chambering, initially a main vertical shaft is sunk
into the rock surrounding the pipe. tunnels are driven
into the pipe from the main shaft at established levels of
600, 1000 and 1600 feet. The ore is retrieved by
blasting and transported to the main shaft and then to
the surface. Levels are worked on, till a seam is
exhausted.
Block caving and chambering are commonly used in diamond mining
where the deposit is a pipe deposit. In general, block caving
techniques are almost completely mechanized; all operations are
carried out in one level only. This gives better yields and higher
levels of safety and efficiency, as against chambering techniques.

River Diggings:
Gemstones which have been deposited in river and lake beds
can be mined by this method.
o Dry Diggings: In this type of mining, a river has either
changed its course naturally or is made to change. This
is done artificially by blocking the river at two ends and
creating a canal to divert the water. In whichever
manner, the rock bed is allowed to dry and then the
gravel is sieved to obtain the gem rough.
o Wet Diggings: In such diggings the gravel is removed
from the flowing river and then sieved to separate the
gem rough.

Sea:
o
Undersea or Marine Mining: This type of mining is
used wherever there are marine deposits. These may be
on the beach, as in the Namaqualand diamond deposits
in West Africa, or they may be off - shore deposits. This
type of mining may involve land reclamation or even
deep sea dredging. Mention must be made of the
organic gem materials and the manner in which they
are retrieved. Amber and Jet are recovered by pit mining
while amber is also fished out of the waters, as is seen
in the Baltic Sea. Corals are collected by divers with
specialized equipment to remove and cart them out.
Pearls are recovered by divers who collect the pearl
bearing mollusks from the sea bed.